Human MEKK proteins, corresponding nucleic acid molecules and uses therefor

ABSTRACT

Isolated nucleic acid molecules encoding human MEKK proteins, and isolated MEKK proteins, are provided. The invention further provides antisense nucleic acid molecules, recombinant expression vectors containing a nucleic acid molecule of the invention, host cells into which the expression vectors have been introduced and non-human transgenic animals carrying a human MEKK transgene. The invention further provides human MEKK fusion proteins and anti-human MEKK antibodies. Methods of using the human MEKK proteins and nucleic acid molecules of the invention are also disclosed, including methods for detecting human MEKK activity in a biological sample, methods of modulating human MEKK activity in a cell, and methods for identifying agents that modulate the activity of human MEKK.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of continuation application Ser. No. 10/000,864 entitled “Human MEKK Proteins, Corresponding Nucleic Acid Molecules and Uses Therefor,” filed Oct. 31, 2001 (pending) which is a continuation of prior-filed application Ser. No. 09/423,890 entitled “Human MEKK Proteins, Corresponding Nucleic Acid Molecules, and Uses Therefor,” filed Mar. 6, 2000 (issued U.S. Pat. No. 6,312,934), which is a U.S. National Stage Entry of PCT/US99/05556, filed Mar. 15, 1999, which claims the benefit of prior-filed provisional application U.S. Patent Application Ser. No. 60/078,153 entitled “Human MEKK2 Nucleic Acid and Protein Molecules and Uses Therefor”, filed Mar. 16, 1998 and of prior-filed provisional application U.S. Patent Application Ser. No. 60/099,165 entitled “Human MEKK3 Protein and Nucleic Acid Molecules and Uses Therefor” filed Sep. 4, 1998. The present application is also related to PCT Patent Application Serial No. PCT/US99/02974, entitled “MEKK1 Proteins and Fragments Thereof for Use in Regulating Apoptosis”, filed Feb. 12, 1999, which claims priority to U.S. application Ser. No. 09/023,130 entitled “Method And Product For Regulating Apoptosis”, filed Feb. 13, 1998. The contents of the above-referenced patent applications are incorporated herein by this reference in its entirety.

FIELD OF THE INVENTION

This invention relates to isolated nucleic acid molecules encoding MEKK proteins, substantially pure MEKK proteins, and products and methods for regulating signal transduction in a cell.

BACKGROUND OF THE INVENTION

Mitogen-activated protein kinase (MAPKs) (also called extracellular signal-regulated kinases or ERKs) are rapidly activated in response to ligand binding by both growth factor receptors that are tyrosine kinases (such as the epidermal growth factor (EGF) receptor) and receptors that are coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) such as the thrombin receptor. In addition, receptors like the T cell receptor (TCR) and B cell receptor (BCR) are non-covalently associated with src family tyrosine kinases which activate MAPK pathways. Specific cytokines such as tumor necrosis factor (TNFα) can also regulate MAPK pathways. The MAPKs appear to integrate multiple intracellular signals transmitted by various second messengers. MAPKs phosphorylate and regulate the activity of enzymes and transcription factors including the EGF receptor, Rsk 90, phospholipase A₂, c-Myc, c-Jun and Elk-1/TCF. Although the rapid activation of MAPKs by receptors that are tyrosine kinases is dependent on Ras, G protein-mediated activation of MAPK appears to occur through pathways dependent and independent of Ras.

The MAPKs are activated by phosphorylation on both a threonine and tyrosine by dual specificity kinases, MAPK/ERK kinases (MEKs) which are, in turn, activated by serine/threonine phosphorylation MAPK kinase kinases (MKKKs or MEKKs). At present, at least four MEKKs have been identified. The four MEKK proteins range from 69.5-185 kDa in size, having their kinase domains in the carboxy-terminal end of the protein and their catalytic domains in the amino-terminal end of the protein. Murine MEKK1 was cloned initially on the basis of its homology with the STE11 and Byr2 kinases from yeast (Lange-Carter et al. (1993) Science 260:315-319; Xu et al. (1996) Proc. Natl. Acad. Sci. USA 93:5291-5295; and Blank et al. (1996) J. Biol. Chem. 271:5361-5368). Murine MEKK2 and MEKK3 were subsequently cloned and found to have 94% homology in their kinase domains as well as 65% homology within their catalytic domains. Blank et al., supra. The cloning of murine MEKK4 revealed approximately 55% homology to the kinase domains of MEKKs 1, 2, and 3 whereas the amino-terminal region of MEKK4 has little sequence homology to the other MEKK family members. Gerwin et al. (1997) J. Biol. Chem. 272:8288-8295. MEKK1 and MEKK4, but not MEKK2 and MEKK3, bind to the low molecular weight GTP-binding proteins Cdc42 and Rac. Furthermore, MEKK1 also binds to Ras in a GTP-dependent manner (Russell et al. (1996) J. Biol. Chem. 11757-11760) and Ras activity is required for EGF-mediated stimulation of MEKK1 activity (Lange-Carter and Johnson (1994) Science 265:1458-1461). In addition to growth factor receptor tyrosine kinases (i.e. EGF receptor), the TNF receptor, the FcεR1 in mast cells Ishizuka et al. et al. (1996) J. Biol. Chem. 271:12762-12766) and the N-formyl methionyl leucine peptide receptor in neutrophils have been shown to activate MEKK1. EGF and TNF also activate MEKK3 and it also appears that the other MEKK proteins are regulated by tyrosine kinase receptors but the intermediate components and effector molecules leading to their activation are poorly understood.

The cellular effects of MEKK1 are quite diverse and can be classified as being either JNK-dependent or JNK-independent. For example, MEKK1 can mediate activation of ERK1 and ERK2 and, by a yet undefined mechanism, activation of the c-Myc transcription factor independent of JNK activity (Lassignal-Johnson et al. (1996) J. Biol Chem. 271:3229-3237 and Lange-Carter et al. (1993) Science 260:315-319). Alternatively, MEKK1 may or may not require JNK activity for activation of IκB kinase which leads to NKκB activation (Liu et al. (1996) Cell 87:565-576 and Meyer et al. (1996) J. Biol. Chem. 271:8971-8976). Furthermore, depending upon the cell type, MEKK1, but not MEKK2, 3 or 4, has been shown to mediate apoptosis by both JNK-dependent and JNK-independent mechanisms (Xia et al. (1995) Science 270:1326-1331 and Lassignal-Johnson et al. (1996) J. Biol Chem. 271:3229-3237).

Given the important role of members of the MAPK signal transduction cascade, in particular the MEKK signal transduction molecules, in regulating mammalian cellular processes ranging from cellular proliferation and differation to cellular apoptosis, there exists a need for identifying human MEKK nucleic acid and protein molecules as well as for modulators of such molecules for use in regulating a variety of human cellular responses.

SUMMARY OF THE INVENTION

This invention provides human MEKK compositions. In particular, this invention provides isolated nucleic acid molecules encoding human MEKK1, human MEKK2, and human MEKK3. The invention further provides isolated human MEKK1, human MEKK2, and human MEKK3 proteins. Because the MEKK compositions of the invention are human-derived, they function optimally in human cells (compared with non-human MEKK compositions) and do not stimulate an immune response in humans.

One aspect of the invention pertains to an isolated nucleic acid molecule having a nucleotide sequence which encodes a human MEKK protein. In a preferred embodiment, the nucleic acid molecule has the nucleotide sequence of SEQ ID NO: 1, SEQ ID NO:3, or SEQ ID NO:5. In other embodiments, the nucleic acid molecule has at least 90-91% nucleotide identity, more preferably 92-93% nucleotide identity, more preferably 94-95% nucleotide identity, more preferably 96-97% nucleotide identity, more preferably 98-99% nucleotide identity, and even more preferably 99.5% nucleotide identity with the nucleotide sequence SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5.

The isolated nucleic acid molecules of the invention encoding human MEKK proteins can be incorporated into a vector, such as an expression vector, and this vector can be introduced into a host cell. The invention also provides a method for producing a human MEKK protein by culturing a host cell of the invention (carrying a huMEKK1, huMEKK2, or huMEKK3 expression vector) in a suitable medium until a human MEKK protein is produced. The method can further involve isolating the human MEKK protein from the medium or the host cell.

Another aspect of the invention pertains to an isolated human MEKK proteins. Preferably, the human MEKK protein has the amino acid sequence of SEQ ID NO:2, SEQ ID NO:4, or SEQ ID NO:6. In other embodiments, the protein has at least 90-91% amino acid identity, more preferably 92-93% amino identity, more preferably 94-95% amino identity, more preferably 96-97% amino identity, more preferably 98-99% amino identity, and even more preferably 99.5% amino acid identity with the amino acid sequence of SEQ ID NO:2, SEQ ID NO:4, or SEQ ID NO:6.

Fusion proteins, including a human MEKK protein operatively linked to a polypeptide other than human MEKK, are also encompassed by the invention, as well as antibodies that specifically bind a human MEKK protein. The antibodies can be, for example, polyclonal antibodies or monoclonal antibodies. In one embodiment, the antibodies are coupled to a detectable substance.

Another aspect of the invention pertains to a nonhuman transgenic animal that contains cells carrying a transgene encoding a human MEKK protein.

Yet another aspect of the invention pertains to a method for detecting the presence of human MEKK in a biological sample. The method involves contacting the biological sample with an agent capable of detecting an indicator of human MEKK activity such that the presence of human MEKK is detected in the biological sample. The invention also provides a method for modulating human MEKK activity in a cell which involves contacting the cell with an agent that modulates human MEKK activity such that human MEKK activity in the cell is modulated.

Still another aspect of the invention pertains to methods for identifying a compound that modulates the activity of a human MEKK protein. These methods generally involve: providing an indicator composition that comprises a human MEKK protein; contacting the indicator composition with a test compound; and determining the effect of the test compound on the activity of the human MEKK protein in the indicator composition to thereby identify a compound that modulates the activity of a human MEKK protein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1B depicts the cDNA sequence of human MEKK1. The nucleic acid sequence corresponds to nucleotides 1 to 3911 of SEQ ID NO:1.

FIG. 2 depicts the amino acid sequence of human MEKK1. The amino acid sequence corresponds to amino acids 1 to 1302 of SEQ ID NO:2.

FIG. 3A-J shows a global alignment of the nucleic acid sequence of human MEKK (SEQ ID NO:1) with the nucleic acid sequence of mouse MEKK1 SEQ ID NO:7).

FIG. 4A-C shows an alignment of the amino acid sequence of human MEKK1 (SEQ ID NO:2) with that of murine MEKK1 (SEQ ID NO:8). Amino acid differences between the two sequences are underlined and bolded.

FIG. 5 depicts the cDNA sequence of human MEKK2. The nucleic acid sequence corresponds to nucleotides 1 to 2013 of SEQ ID NO:3.

FIG. 6 depicts the amino acid sequence of human MEKK2. The amino acid sequence corresponds to amino acids 1 to 619 of SEQ ID NO:4.

FIG. 7A-7E shows a global alignment of the nucleic acid sequences of human MEKK2 (SEQ ID NO:3) and murine MEKK2 (SEQ ID NO:9).

FIG. 8 shows an alignment of the amino acid sequences of human MEKK2 (SEQ ID NO:4) and murine MEKK2 (SEQ ID NO:10).

FIG. 9 depicts the cDNA sequence of human MEKK3. The nucleic acid sequence corresponds to nucleotides 1 to 1935 of SEQ ID NO:5.

FIG. 10 depicts the amino acid sequence of human MEKK3. The amino acid sequence corresponds to amino acids 1 to 626 of SEQ ID NO:6.

FIG. 11A-11G shows a global alignment of the nucleic acid sequences of human MEKK3 (SEQ ID NO:5) and murine MEKK3 (SEQ ID NO:11).

FIG. 12 shows an alignment of the amino acid sequences of human MEKK3 (SEQ ID NO:6) and murine MEKK3 (SEQ ID NO:12).

FIG. 13 shows an alignment of the amino acid sequences of the kinase catalytic domains of murine MEKK1 (corresponding to amino acids 1229-1493 of SEQ ID NO:8), murine MEKK2 (corresponding to amino acids 361-619 of SEQ ID NO:10), murine MEKK3 (corresponding to amino acids 367-626 of SEQ ID NO:12), murine MEKK4 (corresponding to amino acids 1337-1597 of SEQ ID NO:13), human MEKK1 (corresponding to amino acids 1038-1302 of SEQ ID NO:2), human MEKK2 (corresponding to amino acids 361-619 of SEQ ID NO:4), and human MEKK 3 (corresponding to amino acids 367-626 of SEQ ID NO:6). The consensus kinase domains are indicated by the roman numerals I through XI. The most highly conserved residues are underlined.

DETAILED DESCRIPTION OF THE INVENTION

This invention pertains to human MEKK compositions, such as isolated nucleic acid molecules encoding human MEKK1, human MEKK2, and human MEKK3. The invention also pertains to isolated human MEKK proteins (e.g., human MEKK1, human MEKK2, and human MEKK3), as well as methods of use therefor. The human compositions of the invention have the advantages that they function optimally in human cells (compared with non-human MEKK compositions) and do not stimulate an immune response in humans.

So that the invention may be more readily understood, certain terms are first defined.

As used herein, the term “human MEKK protein” is intended to encompass proteins that share the distinguishing structural and functional features (described further herein) of the human MEKK protein having the amino acid sequences of SEQ ID NO: 2, SEQ ID NO:4, and SEQ ID NO:6, including the amino acid residues unique to human MEKK proteins (as compared to mouse MEKK proteins), which are underlined and bolded in FIG. 4, FIG. 8, and FIG. 12.

As used herein, the term “nucleic acid molecule” is intended to include DNA molecules (e.g., cDNA or genomic DNA) and RNA molecules (e.g., mRNA). The nucleic acid molecule may be single-stranded or double-stranded, but preferably is double-stranded DNA.

An used herein, an “isolated nucleic acid molecule” refers to a nucleic acid molecule that is free of gene sequences which naturally flank the nucleic acid in the genomic DNA of the organism from which the nucleic acid is derived (i.e., genetic sequences that are located adjacent to the gene for the isolated nucleic molecule in the genomic DNA of the organism from which the nucleic acid is derived). For example, in various embodiments, an isolated human MEKK nucleic acid molecule typically contains less than about 10 kb of nucleotide sequences which naturally flank the nucleic acid molecule in genomic DNA of the cell from which the nucleic acid is derived, and more preferably contains less than about 5, kb, 4 kb, 3 kb, 2 kb, 1 kb, 0.5 kb or 0.1 kb of naturally flanking nucleotide sequences. An “isolated” human MEKK nucleic acid molecule may, however, be linked to other nucleotide sequences that do not normally flank the human MEKK sequences in genomic DNA (e.g., the human MEKK nucleotide sequences may be linked to vector sequences). In certain preferred embodiments, an “isolated” nucleic acid molecule, such as a cDNA molecule, also may be free of other cellular material. However, it is not necessary for the human MEKK nucleic acid molecule to be free of other cellular material to be considered “isolated” (e.g., a human MEKK DNA molecule separated from other mammalian DNA and inserted into a bacterial cell would still be considered to be “isolated”).

As used herein, the term “hybridizes under high stringency conditions” is intended to describe conditions for hybridization and washing under which nucleotide sequences having substantial homology to each other remain stably hybridized to each other. Preferably, the conditions are such that sequences at least about 70%, more preferably at least about 80%, even more preferably at least about 85% or 90% homologous to each other typically remain hybridized to each other. A preferred, non-limiting example of high stringency conditions are hybridization in a hybridization buffer that contains 6× sodium chloride/sodium citrate (SSC) at a temperature of about 45° C. for several hours to overnight, followed by one or more washes in a washing buffer containing 0.2×SSC, 0.1% SDS at a temperature of about 50-65° C.

To determine the percent homology of two amino acid sequences or of two nucleic acids, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in the sequence of a first amino acid or nucleic acid sequence for optimal alignment with a second amino or nucleic acid sequence and non-homologous sequences can be disregarded for comparison purposes). In a preferred embodiment, the length of a reference sequence aligned for comparison purposes is at least 30%, preferably at least 40%, more preferably at least 50%, even more preferably at least 60%, and even more preferably at least 70%, 80%, or 90% of the entire length of the reference sequence (e.g., when aligning a second sequence to the MEKK amino acid sequence of SEQ ID NO:6 having 626 amino acid residues, at least 188, preferably at least 250, more preferably at least 313, even more preferably at least 376, and even more preferably at least 438, 501 or 563 amino acid residues are aligned). In a more preferred embodiment, the aligned amino acid residues are consecutive (e.g., homologous or identical over 188, 250, 313, 376, 438, 501, or 563 consecutive amino acid residues.) After aligning, the amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are homologous at that position (i.e., as used herein amino acid or nucleic acid “homology” is equivalent to amino acid or nucleic acid “identity”). The percent homology between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % homology=# of identical positions/total # of positions×100).

The comparison of sequences and determination of percent homology between two sequences can be accomplished using a mathematical algorithim. A preferred, non-limiting example of a mathematical algorithim utilized for the comparison of sequences is the algorithm of Karlin and Altschul (1990) Proc. Natl. Acad. Sci. USA 87:2264-68, modified as in Karlin and Altschul (1993) Proc. Natl. Acad. Sci. USA 90:5873-77. Such an algorithm is incorporated into the NBLAST and XBLAST programs (version 2.0) of Altschul, et al. (1990) J. Mol. Biol. 215:403-10. BLAST nucleotide searches can be performed with the NBLAST program, score=100, wordlength=12 to obtain nucleotide sequences homologous to MEKK nucleic acid molecules of the invention. BLAST protein searches can be performed with the XBLAST program, score=50, wordlength=3 to obtain amino acid sequences homologous to MEKK protein molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., (1997) Nucleic Acids Res. 25(17):3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. See http://www.ncbi.nlm.nih.gov.

Another preferred, non-limiting example of a mathematical algorithim utilized for the comparison of sequences is the algorithm of Myers and Miller (1989) CABIOS. Such an algorithm is incorporated into the ALIGN program (version 2.0) which is part of the GCG sequence alignment software package. When utilizing the ALIGN program for comparing amino acid sequences, a PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used. Another preferred, non-limiting example of a mathematical algorithim utilized for the alignment of protein sequences is the Lipman-Pearson algorithm (Lipman and Pearson (1985) Science 227:1435-1441). When using the Lipman-Pearson algorithm, a PAM250 weight residue table, a gap length penalty of 12, a gap penalty of 4, and a Ktuple of 2 can be used. A preferred, non-limiting example of a mathematical algorithim utilized for the alignment of nucleic acid sequences is the Wilbur-Lipman algorithm (Wilbur and Lipman (1983) Proc. Natl. Acad. Sci. USA 80:726-730). When using the Wilbur-Lipman algorithm, a window of 20, gap penalty of 3, Ktuple of 3 can be used. Both the Lipman-Pearson algorithm and the Wilbur-Lipman algorithm are incorporated, for example, into the MEGALIGN program (e.g., version 3.1.7) which is part of the DNASTAR sequence analysis software package.

As used herein, a “naturally-occurring” nucleic acid molecule refers to an RNA or DNA molecule having a nucleotide sequence that occurs in nature (e.g., encodes a natural protein).

As used herein, an “antisense” nucleic acid comprises a nucleotide sequence which is complementary to a “sense” nucleic acid encoding a protein (e.g., complementary to the coding strand of a double-stranded cDNA molecule, complementary to an mRNA sequence or complementary to the coding strand of a gene. Accordingly, an antisense nucleic acid can hydrogen bond to a sense nucleic acid).

As used herein, the term “coding region” refers to regions of a nucleotide sequence comprising codons which are translated into amino acid residues, whereas the term “noncoding region” refers to regions of a nucleotide sequence that are not translated into amino acids (e.g., 5′ and 3′ untranslated regions).

As used herein, the term “vector” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a “plasmid”, which refers to a circular double stranded DNA loop into which additional DNA segments may be ligated. Another type of vector is a viral vector, wherein additional DNA segments may be ligated into the viral genome. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) are integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively linked. Such vectors are referred to herein as “recombinant expression vectors” or simply “expression vectors”. In general, expression vectors of utility in recombinant DNA techniques are often in the form of plasmids. In the present specification, “plasmid” and “vector” may be used interchangeably as the plasmid is the most commonly used form of vector. However, the invention is intended to include such other forms of expression vectors, such as viral vectors (e.g., replication defective retroviruses, adenoviruses and adeno-associated viruses), which serve equivalent functions.

As used herein, the term “host cell” is intended to refer to a cell into which a nucleic acid of the invention, such as a recombinant expression vector of the invention, has been introduced. The terms “host cell” and “recombinant host cell” are used interchangeably herein. It should be understood that such terms refer not only to the particular subject cell but to the progeny or potential progeny of such a cell. Because certain modifications may occur in succeeding generations due to either mutation or environmental influences, such progeny may not, in fact, be identical to the parent cell, but are still included within the scope of the term as used herein.

As used herein, a “transgenic animal” refers to a non-human animal, preferably a mammal, more preferably a mouse, in which one or more of the cells of the animal includes a “transgene”. The term “transgene” refers to exogenous DNA which is integrated into the genome of a cell from which a transgenic animal develops and which remains in the genome of the mature animal, for example directing the expression of an encoded gene product in one or more cell types or tissues of the transgenic animal.

As used herein, a “homologous recombinant animal” refers to a type of transgenic non-human animal, preferably a mammal, more preferably a mouse, in which an endogenous gene has been altered by homologous recombination between the endogenous gene and an exogenous DNA molecule introduced into a cell of the animal, e.g., an embryonic cell of the animal, prior to development of the animal.

As used herein, an “isolated protein” refers to a protein that is substantially free of other proteins, cellular material and culture medium when isolated from cells or produced by recombinant DNA techniques, or chemical precursors or other chemicals when chemically synthesized.

In one embodiment, a MEKK protein is identified based on the presence of at least a “catalytic domain ” in the protein or corresponding nucleic acid molecule. As used herein, the term “catalytic domain” refers to a protein domain consisting of at least about 150-400, preferably about 200-350, more preferably about 220-300, even more preferably at least about 240-280, and even more preferably about 260 amino acid residues in length. In one embodiment, a MEKK catalytic domain contains at least about 9-13, preferably about 10-12, and more preferably about 11 consensus kinase domains which are conserved among MEKK protein family members. Such consensus kinase domains are indicated by roman numerals in FIG. 13. Particularly conserved residues within the consensus kinase domains are underlined. A consensus kinase domain is further defined in Hanks et al. (1988) Science 241:42-52. In another embodiment, a MEKK catalytic domain is identified based in its ability to retain a functional activity of a MEKK protein, particularly a MEKK protein (e.g., retains the ability to phosphorylate a MEKK substrate) even in the absence of a MEKK regulatory domain, defined herein.

In another embodiment, a MEKK protein is identified based on the presence of at least a “regulatory domain ” in the protein or corresponding nucleic acid molecule. As used herein, the term “regulatory domain” refers to a protein domain consisting of at least about 250-500, preferably about 300-450, more preferably about 320-400, even more preferably at least about 340-380, and even more preferably about 360 amino acid residues in length, of which at least 10%, preferably about 15%, and more preferably about 20% of the amino acid residues are serine and/or threonone residues. In another embodiment, a MEKK regulatory domain is identified based on its ability to regulate the activity of a MEKK catalytic domain. In one exemplary embodiment, a MEKK regulatory domain is capable of binding a MEKK binding partner such that the activity of a MEKK protein is modulated.

As used interchangeably herein, a “MEKK activity”, “functional activity of MEKK”, or “biological activity of MEKK”, refers to an activity exerted by a MEKK protein, polypeptide or nucleic acid molecule as determined in vivo, or in vitro, according to standard techniques. In one embodiment, a MEKK activity is a direct activity, such as an association with a MEKK-target molecule. As used herein, a “target molecule” is a molecule with which a MEKK protein binds or interacts in nature, such that MEKK-mediated function is achieved. A MEKK target molecule can be a MEKK protein or polypeptide of the present invention or a non-MEKK molecule. For example, a MEKK target molecule can be a non-MEKK protein molecule (e.g. a MEKK binding partner such as a Ras protein, or a MEKK substrate such as a MEK protein). As used herein, a “MEKK” substrate is a molecule with which a MEKK protein interacts in vivo or in vitro such that the MEKK substrate is phosphorylated by the enzymatic activity of the MEKK protein. Also as used herein, a MEKK “binding partner” is a molecule with which a MEKK protein interacts in vivo or in vitro such that the enzymatic activity of the MEKK protein is effected. Alternatively, a MEKK activity is an indirect activity, such as an activity mediated by interaction of the MEKK protein with a MEKK target molecule such that the target molecule modulates a downstream cellular activity (e.g., MAPK activity).

In a preferred embodiment, a MEKK activity is at least one or more of the following activities: (i) interaction of a MEKK protein with a MEKK target molecule, wherein the target molecule effects the activity of the MEKK molecule; (ii) interaction of a MEKK protein with a MEKK target molecule, wherein the MEKK molecule effects the activity of the target molecule; (iii) phosphorylation of a MEKK target molecule (e.g., MEK or JNK kinase); (iv) activation of a MEKK target molecule (e.g., MEK or JNK kinase); (v) mediation of activation of MAPK signal transduction molecules (e.g., c-Jun kinase (JNK) or p42/p44^(MAPK)); (vi) autophosphorylation of MEKK; (vii) autoactivation of MEKK 3; and (viii) modulation of the activity of a nuclear transcription factor (e.g., ATF 2).

Accordingly, another embodiment of the invention features isolated MEKK proteins and polypeptides having a MEKK activity. Preferred proteins are MEKK proteins having at least a MEKK catalytic domain and, preferably, a MEKK activity. Additional preferred proteins are MEKK proteins having at least a MEKK regulatory domain and, preferably, a MEKK activity. In another preferred embodiment, the isolated protein is a MEKK protein having a MEKK catalytic domain, a MEKK regulatory domain, and a MEKK activity.

As used herein, the term “antibody” is intended to include immunoglobulin molecules and immunologically active portions of immunoglobulin molecules, i.e., molecules that contain an antigen binding site which specifically binds (immunoreacts with) an antigen, such as Fab and F(ab′)₂ fragments. The terms “monoclonal antibodies” and “monoclonal antibody composition”, as used herein, refer to a population of antibody molecules that contain only one species of an antigen binding site capable of immunoreacting with a particular epitope of an antigen, whereas the term “polyclonal antibodies” and “polyclonal antibody composition” refer to a population of antibody molecules that contain multiple species of antigen binding sites capable of interacing with a particular antigen. A monoclonal antibody compositions thus typically display a single binding affinity for a particular antigen with which it immunoreacts.

There is a known and definite correspondence between the amino acid sequence of a particular protein and the nucleotide sequences that can code for the protein, as defined by the genetic code (shown below). Likewise, there is a known and definite correspondence between the nucleotide sequence of a particular nucleic acid molecule and the amino acid sequence encoded by that nucleic acid molecule, as defined by the genetic code. GENETIC CODE Alanine (Ala, A) GCA, GCC, GCG, GCT Arginine (Arg, R) AGA, ACG, CGA, CGC, CGG, CGT Asparagine (Asn, N) AAC, AAT Aspartic acid (Asp,D) GAC, GAT Cysteine (Cys, C) TGC, TGT Glutamic acid (Glu,E) GAA, GAG Glutamine (Gln, Q) CAA, CAG Glycine (Gly, G) GGA, GGC, GGG, GGT Histidine (His, H) CAC, CAT Isoleucine (Ile, I) ATA, ATC, ATT Leucine (Leu, L) CTA, CTC, CTG, CTT, TTA, TTG Lysine (Lys, K) AAA, AAG Methionine (Met, M) ATG Phenylalanine (Phe,F) TTC, TTT Proline (Pro, P) CCA, CCC, CCG, CCT Serine (Ser, S) AGC, AGT, TCA, TCC, TCG, TCT Threonine (Thr, T) ACA, ACC, ACG, ACT Tryptophan (Trp, W) TGG Tyrosine (Tyr, Y) TAC, TAT Valine (Val, V) GTA, GTC, GTG, GTT Termination signal (end) TAA, TAG, TGA

An important and well known feature of the genetic code is its redundancy, whereby, for most of the amino acids used to make proteins, more than one coding nucleotide triplet may be employed (illustrated above). Therefore, a number of different nucleotide sequences may code for a given amino acid sequence. Such nucleotide sequences are considered functionally equivalent since they result in the production of the same amino acid sequence in all organisms (although certain organisms may translate some sequences more efficiently than they do others). Moreover, occasionally, a methylated variant of a purine or pyrimidine may be found in a given nucleotide sequence. Such methylations do not affect the coding relationship between the trinucleotide codon and the corresponding amino acid.

In view of the foregoing, the nucleotide sequence of a DNA or RNA molecule coding for a human MEKK protein of the invention (or any portion thereof) can be used to derive the human MEKK amino acid sequence, using the genetic code to translate the DNA or RNA molecule into an amino acid sequence. Likewise, for any human MEKK-amino acid sequence, corresponding nucleotide sequences that can encode the human MEKK protein can be deduced from the genetic code (which, because of its redundancy, will produce multiple nucleic acid sequences for any given amino acid sequence). Thus, description and/or disclosure herein of a human MEKK nucleotide sequence should be considered to also include description and/or disclosure of the amino acid sequence encoded by the nucleotide sequence. Similarly, description and/or disclosure of a human MEKK amino acid sequence herein should be considered to also include description and/or disclosure of all possible nucleotide sequences that can encode the amino acid sequence.

The human MEKK1 cDNA, which is approximately 3911 nucleotides in length, encodes a protein which is approximately 1302 amino acid residues in length. The coding region is from nucleotide 3 to 3908 of SEQ ID NO:1. The human MEKK1 protein has at least a catalytic domain. A catalytic domain includes, for example, about amino acids 1038-1302 of SEQ ID NO:2 (e.g. catalytic domain having 259 or 260-265 amino acid residues). Catalytic domains having 100, 150, 200, or 250 consecutive amino acids from about amino acids 1038-1302 of SEQ ID NO:2 are also intended to be within the scope of the invention. The human MEKK1 protein further has at least a regulatory domain. A regulatory domain includes, for example, about amino acids xx-xxx of SEQ ID NO:2. Regulatory domains having 200, 250, 300, or 350 consecutive amino acids from about amino acids xx-xxx of SEQ ID NO:2 are also intended to be within the scope of the invention. Also intended to be within the scope of the invention are modified catalytic and regulatory domains having about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 116, 117, 118, 119, 120, 121, 122, 123, 145, 125 amino acid substitutions, insertions, and/or deletions when compared to the amino acid sequence of SEQ ID NO:2, wherein the modified catalytic or regulatory domain retains the function of a MEKK catalytic or regulatory domain of SEQ ID NO:2.

The human MEKK2 cDNA, which is approximately 2013 nucleotides in length, encodes a protein which is approximately 619 amino acid residues in length. The coding region is from nucleotide 124 to 1980 of SEQ ID NO:3. The human MEKK2 protein has at least a catalytic domain. A catalytic domain includes, for example, about amino acids 361-619 of SEQ ID NO:4. Catalytic domains having 100, 150, 200, or 250 consecutive amino acids from about amino acids 361-619 of SEQ ID NO:4 are also intended to be within the scope of the invention. The human MEKK2 protein further has at least a regulatory domain. A regulatory domain includes, for example, about amino acids 1-360 of SEQ ID NO:4. Regulatory domains having 200, 250, 300, or 350 consecutive amino acids from about amino acids 1-360 of SEQ ID NO:4 are also intended to be within the scope of the invention. Also intended to be within the scope of the invention are modified catalytic and regulatory domains having about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 61, or 62 amino acid substitutions, insertions, and/or deletions when compared to the amino acid sequence of SEQ ID NO:4, wherein the modified catalytic or regulatory domain retains the function of a MEKK catalytic or regualtory doamin of SEQ ID NO:4.

The human MEKK3 cDNA, which is approximately 1935 nucleotides in length, encodes a protein which is approximately 626 amino acid residues in length. The coding region is from nucleotide 25 to 1902 of SEQ ID NO:5. The human MEKK3 protein has at least a catalytic domain. A catalytic domain includes, for example, about amino acids 367-626 of SEQ ID NO:6. Catalytic domains having 100, 150, 200, or 250 consecutive amino acids from about amino acids 367-626 of SEQ ID NO:6 are also intended to be within the scope of the invention. The human MEKK3 protein further has at least a regulatory domain. A regulatory domain includes, for example, about amino acids 1-366 of SEQ ID NO:6. Regulatory domains having 200, 250, 300, or 350 consecutive amino acids from about amino acids 1-366 of SEQ ID NO:6 are also intended to be within the scope of the invention. Also intended to be within the scope of the invention are modified catalytic and regulatory domains having about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, or 40 amino acid substitutions, insertions, and/or deletions when compared to the amino acid sequence of SEQ ID NO:6, wherein the modified catalytic or regulatory domain retains the function of a MEKK catalytic or regualtory doamin of SEQ ID NO:6.

Various aspects of the invention are described in further detail in the following subsections:

I. Isolated Nucleic Acid Molecules

One aspect of the invention pertains to isolated nucleic acid molecules that encode human MEKK proteins. The nucleotide sequence of human MEKK1, and corresponding predicted amino acid sequence, are shown in SEQ ID NOs:1 and 2, respectively. The nucleotide sequence of human MEKK2, and corresponding predicted amino acid sequence, are shown in SEQ ID NOs:3 and 4, respectively. The nucleotide sequence of human MEKK3, and corresponding predicted amino acid sequence, are shown in SEQ ID NOs:5 and 6, respectively. In a preferred embodiment, the nucleic acid molecule comprises the nucleotide sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5. In other embodiments, the nucleic acid molecule has at least 90-91% nucleotide identity, more preferably 92-93% nucleotide identity, more preferably 94-95% nucleotide identity, more preferably 96-97% nucleotide identity, more preferably 98-99% nucleotide identity, and even more preferably 99.5% nucleotide identity with the nucleotide sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5.

Nucleic acid molecules that differ from SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5 due to degeneracy of the genetic code, and thus encode the same human MEKK protein as that encoded by SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5, are encompassed by the invention. Accordingly, in another embodiment, an isolated nucleic acid molecule of the invention has a nucleotide sequence encoding a protein having an amino acid sequence shown in SEQ ID NO:2, SEQ ID NO:4, or SEQ ID NO:6.

A nucleic acid molecule having the nucleotide sequence of human MEKK1, human MEKK2, or human MEKK3 can be isolated using standard molecular biology techniques and the sequence information provided herein. For example, a human MEKK DNA can be isolated from a human genomic DNA library using all or portion of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5 as a hybridization probe and standard hybridization techniques (e.g., as described in Sambrook, J., et al. Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1989). Moreover, a nucleic acid molecule encompassing all or a portion of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5 can be isolated by the polymerase chain reaction using oligonucleotide primers designed based upon the sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5. For example, mRNA can be isolated from cells (e.g., by the guanidinium-thiocyanate extraction procedure of Chirgwin et al. (1979) Biochemistry 18: 5294-5299) and cDNA can be prepared using reverse transcriptase (e.g., Moloney MLV reverse transcriptase, available from Gibco/BRL, Bethesda, Md.; or AMV reverse transcriptase, available from Seikagaku America, Inc., St. Petersburg, Fla.). Synthetic oligonucleotide primers for PCR amplification can be designed based upon the nucleotide sequence shown in SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5. A nucleic acid of the invention can be amplified using cDNA or, alternatively, genomic DNA, as a template and appropriate oligonucleotide primers according to standard PCR amplification techniques. The nucleic acid so amplified can be cloned into an appropriate vector and characterized by DNA sequence analysis. Furthermore, oligonucleotides corresponding to a human MEKK nucleotide sequence can be prepared by standard synthetic techniques, e.g., using an automated DNA synthesizer.

In addition to the human MEKK nucleotide sequence shown in SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5, it will be appreciated by those skilled in the art that DNA sequence polymorphisms that lead to minor changes in the nucleotide or amino acid sequences of human MEKK may exist within a population. Such genetic polymorphism in the human MEKK gene may exist among individuals within a population due to natural allelic variation. Such natural allelic variations can typically result in 1-2% variance in the nucleotide sequence of the a gene. Any and all such nucleotide variations and resulting amino acid polymorphisms in human MEKK that are the result of natural allelic variation and that do not alter the functional activity of human MEKK are intended to be within the scope of the invention.

Nucleic acid molecules corresponding to natural allelic variants of the human MEKK DNAs of the invention can be isolated based on their homology to the human MEKK nucleic acid molecules disclosed herein using the human DNA, or a portion thereof, as a hybridization probe according to standard hybridization techniques under high stringency hybridization conditions. Accordingly, in another embodiment, an isolated nucleic acid molecule of the invention hybridizes under high stringency conditions to a second nucleic acid molecule comprising the nucleotide sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5. In certain embodiment, the isolated nucleic acid molecule comprises at least 30, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000 or 3000 contiguous nucleotides of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5. Preferably, an isolated nucleic acid molecule of the invention that hybridizes under high stringency conditions to the sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5 corresponds to a naturally-occurring allelic variant of a human MEKK nucleic acid molecule.

In addition to naturally-occurring allelic variants of the human MEKK sequence that may exist in the population, the skilled artisan will further appreciate that minor changes may be introduced by mutation into the nucleotide sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5, thereby leading to changes in the amino acid sequence of the encoded protein, without altering the functional activity of the human MEKK protein. For example, nucleotide substitutions leading to amino acid substitutions at “non-essential” amino acid residues may be made in the sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5. A “non-essential” amino acid residue is a residue that can be altered from the wild-type sequence of human MEKK (e.g., the sequence of SEQ ID NO:2, SEQ ID NO:4, or SEQ ID NO:6) without altering the functional activity of MEKK, whereas an “essential” amino acid residue is required for functional activity.

Accordingly, another aspect of the invention pertains to nucleic acid molecules encoding human MEKK proteins that contain changes in amino acid residues that are not essential for human MEKK activity. Such human MEKK proteins differ in amino acid sequence from SEQ ID NO:2, SEQ ID NO:4, or SEQ ID NO:6 yet retain human MEKK activity. These non-natural variants of human MEKK also differ from non-human MEKK proteins (e.g., mouse or rat MEKK) in that they encode at least one amino acid residue that is unique to human MEKK (i.e., at least one residue that is not present in mouse or rat MEKK). Preferably, these non-natural variants of human MEKK encode at least 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid residues that are unique to human MEKK (i.e., that are not present in mouse or rat MEKK).

An isolated nucleic acid molecule encoding a non-natural variant of a human MEKK protein can be created by introducing one or more nucleotide substitutions, additions or deletions into the nucleotide sequence of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5 (or plasmid pHu-MEKK) such that one or more amino acid substitutions, additions or deletions are introduced into the encoded protein. Mutations can be introduced into SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5 by standard techniques, such as site-directed mutagenesis and PCR-mediated mutagenesis. Preferably, conservative amino acid substitutions are made at one or more non-essential amino acid residues. A “conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art, including basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g. aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). Thus, a nonessential amino acid residue in human MEKK is preferably replaced with another amino acid residue from the same side chain family. Alternatively, in another embodiment, mutations can be introduced randomly along all or part of the human MEKK coding sequence, such as by saturation mutagenesis, and the resultant mutants can be screened for their ability to bind to DNA and/or activate transcription, to identify mutants that retain functional activity. Following mutagenesis, the encoded human MEKK mutant protein can be expressed recombinantly in a host cell and the functional activity of the mutant protein can be determined using assays available in the art for assessing MEKK activity (e.g., assays such as those described in detail in PCT Publication WO 97/39721 and/or asays described in Blank et al. (1996) J. Biol. Chem. 271:5361-5368.

Another aspect of the invention pertains to isolated nucleic acid molecules that are antisense to the coding strand of a human MEKK mRNA or gene. An antisense nucleic acid of the invention can be complementary to an entire human MEKK coding strand, or to only a portion thereof. In one embodiment, an antisense nucleic acid molecule is antisense to a coding region of the coding strand of a nucleotide sequence encoding human MEKK that is unique to human MEKK (as compared to non-human MEKKs, such as mouse or rat MEKK). In another embodiment, the antisense nucleic acid molecule is antisense to a noncoding region of the coding strand of a nucleotide sequence encoding human MEKK that is unique to human MEKK (as compared to non-human MEKKs, such as mouse or rat MEKK). In preferred embodiments, an antisense of the invention comprises at least 30 contiguous nucleotides of the noncoding strand of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5, more preferably at least 50, 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1000 contiguous nucleotides of the noncoding strand of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5.

Given the coding strand sequences encoding human MEKK disclosed herein (e.g., nucleotides 3 to 3908 of SEQ ID NO:1, nucleotides 124-1980 of SEQ ID NO:3, or nucleotides 25-1902 of SEQ ID NO:5), antisense nucleic acids of the invention can be designed according to the rules of Watson and Crick base pairing. The antisense nucleic acid molecule may be complementary to the entire coding region of human MEKK mRNA, or alternatively can be an oligonucleotide which is antisense to only a portion of the coding or noncoding region of human MEKK mRNA. For example, the antisense oligonucleotide may be complementary to the region surrounding the translation start site of human MEKK mRNA. An antisense oligonucleotide can be, for example, about 15, 20, 25, 30, 35, 40, 45 or 50 nucleotides in length. An antisense nucleic acid of the invention can be constructed using chemical synthesis and enzymatic ligation reactions using procedures known in the art. For example, an antisense nucleic acid (e.g., an antisense oligonucleotide) can be chemically synthesized using naturally occurring nucleotides or variously modified nucleotides designed to increase the biological stability of the molecules or to increase the physical stability of the duplex formed between the antisense and sense nucleic acids, e.g., phosphorothioate derivatives and acridine substituted nucleotides can be used. Alternatively, the antisense nucleic acid can be produced biologically using an expression vector into which a nucleic acid has been subcloned in an antisense orientation (i.e., RNA transcribed from the inserted nucleic acid will be of an antisense orientation to a target nucleic acid of interest, described further in the following subsection).

In another embodiment, an antisense nucleic acid of the invention is a ribozyme. Ribozymes are catalytic RNA molecules with ribonuclease activity which are capable of cleaving a single-stranded nucleic acid, such as an mRNA, to which they have a complementary region. A ribozyme having specificity for a human MEKK-encoding nucleic acid can be designed based upon the nucleotide sequence of a human MEKK gene disclosed herein. For example, a derivative of a Tetrahymena L-19 IVS RNA can be constructed in which the base sequence of the active site is complementary to the base sequence to be cleaved in a human MEKK-encoding mRNA. See for example Cech et al. U.S. Pat. No. 4,987,071; and Cech et al. U.S. Pat. No. 5,116,742. Alternatively, human MEKK mRNA can be used to select a catalytic RNA having a specific ribonuclease activity from a pool of RNA molecules. See for example Bartel, D. and Szostak, J. W. (1993) Science 261: 1411-1418.

Yet another aspect of the invention pertains to isolated nucleic acid molecules encoding human MEKK fusion proteins. Such nucleic acid molecules, comprising at least a first nucleotide sequence encoding a human MEKK protein, polypeptide or peptide operatively linked to a second nucleotide sequence encoding a non-human MEKK protein, polypeptide or peptide, can be prepared by standard recombinant DNA techniques. Human MEKK fusion proteins are described in further detail below in subsection III.

II. Recombinant Expression Vectors and Host Cells

Another aspect of the invention pertains to vectors, preferably recombinant expression vectors, containing a nucleic acid encoding human MEKK (or a portion thereof). The expression vectors of the invention comprise a nucleic acid of the invention in a form suitable for expression of the nucleic acid in a host cell, which means that the recombinant expression vectors include one or more regulatory sequences, selected on the basis of the host cells to be used for expression, which is operatively linked to the nucleic acid sequence to be expressed. Within a recombinant expression vector, “operably linked” is intended to mean that the nucleotide sequence of interest is linked to the regulatory sequence(s) in a manner which allows for expression of the nucleotide sequence (e.g., in an in vitro transcription/translation system or in a host cell when the vector is introduced into the host cell). The term “regulatory sequence” is intended to includes promoters, enhancers and other expression control elements (e.g., polyadenylation signals). Such regulatory sequences are described, for example, in Goeddel; Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990). Regulatory sequences include those which direct constitutive expression of a nucleotide sequence in many types of host cell and those which direct expression of the nucleotide sequence only in certain host cells (e.g., tissue-specific regulatory sequences). It will be appreciated by those skilled in the art that the design of the expression vector may depend on such factors as the choice of the host cell to be transformed, the level of expression of protein desired, etc. The expression vectors of the invention can be introduced into host cells to thereby produce proteins or peptides, including fusion proteins or peptides, encoded by nucleic acids as described herein (e.g., human MEKK proteins, mutant forms of human MEKK proteins, human MEKK fusion proteins and the like).

The recombinant expression vectors of the invention can be designed for expression of human MEKK protein in prokaryotic or eukaryotic cells. For example, human MEKK can be expressed in bacterial cells such as E. coli, insect cells (using baculovirus expression vectors) yeast cells or mammalian cells. Suitable host cells are discussed further in Goeddel, Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990). Alternatively, the recombinant expression vector may be transcribed and translated in vitro, for example using T7 promoter regulatory sequences and T7 polymerase.

Expression of proteins in prokaryotes is most often carried out in E. coli with vectors containing constitutive or inducible promotors directing the expression of either fusion or non-fusion proteins. Fusion vectors add a number of amino acids to a protein encoded therein, usually to the amino terminus of the recombinant protein. Such fusion vectors can serve one or more purposes: 1) to increase expression of recombinant protein; 2) to increase the solubility of the recombinant protein; 3) to aid in the purification of the recombinant protein by acting as a ligand in affinity purification; 4) to provide an epitope tag to aid in detection and/or purification of the protein; and/or 5) to provide a marker to aid in detection of the protein (e.g., a color marker using β-galactosidase fusions). Often, in fusion expression vectors, a proteolytic cleavage site is introduced at the junction of the fusion moiety and the recombinant protein to enable separation of the recombinant protein from the fusion moiety subsequent to purification of the fusion protein. Such enzymes, and their cognate recognition sequences, include Factor Xa, thrombin and enterokinase. Typical fusion expression vectors include pGEX (Pharmacia Biotech Inc.; Smith, D. B. and Johnson, K. S. (1988) Gene 67:31-40), pMAL (New England Biolabs, Beverly, Mass.) and pRIT5 (Pharmacia, Piscataway, N.J.) which fuse glutathione S-transferase (GST), maltose E binding protein, or protein A, respectively, to the target recombinant protein. Recombinant proteins also can be expressed in eukaryotic cells as fusion proteins for the same purposes discussed above.

Examples of suitable inducible non-fusion E. coli expression vectors include pTrc (Amann et al., (1988) Gene 69:301-315) and pET 11d (Studier et al., Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990) 60-89). Target gene expression from the pTrc vector relies on host RNA polymerase transcription from a hybrid trp-lac fusion promoter. Target gene expression from the pET 11d vector relies on transcription from a T7 gn10-lac fusion promoter mediated by a coexpressed viral RNA polymerase (T7 gn1). This viral polymerase is supplied by host strains BL21(DE3) or HMS174(DE3) from a resident λ prophage harboring a T7 gn1 gene under the transcriptional control of the lacUV 5 promoter.

One strategy to maximize recombinant protein expression in E. coli is to express the protein in a host bacteria with an impaired capacity to proteolytically cleave the recombinant protein (Gottesman, S., Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990) 119-128). Another strategy is to alter the nucleic acid sequence of the nucleic acid to be inserted into an expression vector so that the individual codons for each amino acid are those preferentially utilized in E. coli (Wada et al., (1992) Nuc. Acids Res. 20:2111-2118). Such alteration of nucleic acid sequences of the invention can be carried out by standard DNA synthesis techniques.

In another embodiment, the human MEKK expression vector is a yeast expression vector. Examples of vectors for expression in yeast S. cerivisae include pYepSec1 (Baldari. et al., (1987) EMBO J. 6:229-234), pMFa (Kurjan and Herskowitz, (1982) Cell 30:933-943), pJRY88 (Schultz et al., (1987) Gene 54:113-123), and pYES2 (Invitrogen Corporation, San Diego, Calif.).

Alternatively, human MEKK can be expressed in insect cells using baculovirus expression vectors. Baculovirus vectors available for expression of proteins in cultured insect cells (e.g., Sf 9 cells) include the pAc series (Smith et al., (1983) Mol. Cell Biol. 3:2156-2165) and the pVL series (Lucklow, V. A., and Summers, M. D., (1989) Virology 170:31-39).

In yet another embodiment, a nucleic acid of the invention is expressed in mammalian cells using a mammalian expression vector. Examples of mammalian expression vectors include pMex-NeoI, pCDM8 (Seed, B., (1987) Nature 329:840) and pMT2PC (Kaufman et al. (1987), EMBO J. 6:187-195). When used in mammalian cells, the expression vector's control functions are often provided by viral regulatory elements. For example, commonly used promoters are derived from polyoma, Adenovirus 2, cytomegalovirus and Simian Virus 40.

In another embodiment, the recombinant mammalian expression vector is capable of directing expression of the nucleic acid preferentially in a particular cell type (e.g., tissue-specific regulatory elements are used to express the nucleic acid). Tissue-specific regulatory elements are known in the art. Non-limiting examples of suitable tissue-specific promoters include lymphoid-specific promoters (Calame and Eaton (1988) Adv. Immunol. 43:235-275), in particular promoters of T cell receptors (Winoto and Baltimore (1989) EMBO J. 8:729-733) and immunoglobulins (Baneiji et al. (1983) Cell 33:729-740; Queen and Baltimore (1983) Cell 33:741-748), the albumin promoter (liver-specific; Pinkert et al. (1987) Genes Dev. 1:268-277), neuron-specific promoters (e.g., the neurofilament promoter; Byrne and Ruddle (1989) Proc. Natl. Acad. Sci. USA 86:5473-5477), pancreas-specific promoters (Edlund et al. (1985) Science 230:912-916), and mammary gland-specific promoters (e.g., milk whey promoter; U.S. Pat. No. 4,873,316 and European Application Publication No. 264,166). Developmentally-regulated promoters are also encompassed, for example the murine hox promoters (Kessel and Gruss (1990) Science 249:374-379) and the α-fetoprotein promoter (Campes and Tilghman (1989) Genes Dev. 3:537-546).

Moreover, inducible regulatory systems for use in mammalian cells are known in the art, for example systems in which gene expression is regulated by heavy metal ions (see e.g., Mayo et al. (1982) Cell 29:99-108; Brinster et al. (1982) Nature 296:39-42; Searle et al. (1985) Mol. Cell. Biol. 5:1480-1489), heat shock (see e.g., Nouer et al. (1991) in Heat Shock Response, e.d. Nouer, L. , CRC, Boca Raton, Fla., pp167-220), hormones (see e.g., Lee et al. (1981) Nature 294:228-232; Hynes et al. (1981) Proc. Natl. Acad. Sci. USA 78:2038-2042; Klock et al. (1987) Nature 329:734-736; Israel & Kaufman (1989) Nucl. Acids Res. 17:2589-2604; and PCT Publication No. WO 93/23431), FK506-related molecules (see e.g., PCT Publication No. WO 94/18317) or tetracyclines (Gossen, M. and Bujard, H. (1992) Proc. Natl. Acad. Sci. USA 89:5547-5551; Gossen, M. et al. (1995) Science 268:1766-1769; PCT Publication No. WO 94/29442; and PCT Publication No. WO 96/01313). Accordingly, in another embodiment, the invention provides a recombinant expression vector in which human MEKK DNA is operatively linked to an inducible eukaryotic promoter, thereby allowing for inducible expression of human MEKK protein in eukaryotic cells.

The invention further provides a recombinant expression vector comprising a DNA molecule of the invention cloned into the expression vector in an antisense orientation. That is, the DNA molecule is operatively linked to a regulatory sequence in a manner which allows for expression (by transcription of the DNA molecule) of an RNA molecule which is antisense to human MEKK mRNA. Regulatory sequences operatively linked to a nucleic acid cloned in the antisense orientation can be chosen which direct the continuous expression of the antisense RNA molecule in a variety of cell types, for instance viral promoters and/or enhancers, or regulatory sequences can be chosen which direct constitutive, tissue specific or cell type specific expression of antisense RNA. The antisense expression vector can be in the form of a recombinant plasmid, phagemid or attenuated virus in which antisense nucleic acids are produced under the control of a high efficiency regulatory region, the activity of which can be determined by the cell type into which the vector is introduced. For a discussion of the regulation of gene expression using antisense genes see Weintraub, H. et al., Antisense RNA as a molecular tool for genetic analysis, Reviews-Trends in Genetics, Vol. 1(1) 1986.

Another aspect of the invention pertains to recombinant host cells into which a vector, preferably a recombinant expression vector, of the invention has been introduced. A host cell may be any prokaryotic or eukaryotic cell. For example, human MEKK protein may be expressed in bacterial cells such as E. coli, insect cells, yeast or mammalian cells (such as Chinese hamster ovary cells (CHO) or COS cells). Other suitable host cells are known to those skilled in the art. Vector DNA can be introduced into prokaryotic or eukaryotic cells via conventional transformation or transfection techniques. As used herein, the terms “transformation” and “transfection” are intended to refer to a variety of art-recognized techniques for introducing foreign nucleic acid (e.g., DNA) into a host cell, including calcium phosphate or calcium chloride co-precipitation, DEAE-dextran-mediated transfection, lipofection, or electroporation. Suitable methods for transforming or transfecting host cells can be found in Sambrook et al. (Molecular Cloning: A Laboratory Manual, 2nd Edition, Cold Spring Harbor Laboratory press (1989)), and other laboratory manuals.

For stable transfection of mammalian cells, it is known that, depending upon the expression vector and transfection technique used, only a small fraction of cells may integrate the foreign DNA into their genome. In order to identify and select these integrants, a gene that encodes a selectable marker (e.g., resistance to antibiotics) is generally introduced into the host cells along with the gene of interest. Preferred selectable markers include those which confer resistance to drugs, such as G418, hygromycin and methotrexate. Nucleic acid encoding a selectable marker may be introduced into a host cell on the same vector as that encoding human MEKK or may be introduced on a separate vector. Cells stably transfected with the introduced nucleic acid can be identified by drug selection (e.g., cells that have incorporated the selectable marker gene will survive, while the other cells die).

A host cell of the invention, such as a prokaryotic or eukaryotic host cell in culture, can be used to produce (i.e., express) human MEKK protein. Accordingly, the invention further provides methods for producing human MEKK protein using the host cells of the invention. In one embodiment, the method comprises culturing the host cell of invention (into which a recombinant expression vector encoding human MEKK has been introduced) in a suitable medium until human MEKK is produced. In another embodiment, the method further comprises isolating human MEKK from the medium or the host cell. In its native form the human MEKK protein is an intracellular protein and, accordingly, recombinant human MEKK protein can be expressed intracellularly in a recombinant host cell and then isolated from the host cell, e.g., by lysing the host cell and recovering the recombinant human MEKK protein from the lysate. Alternatively, recombinant human MEKK protein can be prepared as a extracellular protein by operatively linking a heterologous signal sequence to the amino-terminus of the protein such that the protein is secreted from the host cells. In this case, recombinant human MEKK protein can be recovered from the culture medium in which the cells are cultured.

Certain host cells of the invention can also be used to produce nonhuman transgenic animals. For example, in one embodiment, a host cell of the invention is a fertilized oocyte or an embryonic stem cell into which human MEKK-coding sequences have been introduced. Such host cells can then be used to create non-human transgenic animals in which exogenous human MEKK sequences have been introduced into their genome or homologous recombinant animals in which endogenous MEKK sequences have been altered. Such animals are useful for studying the function and/or activity of human MEKK and for identifying and/or evaluating modulators of human MEKK activity. Accordingly, another aspect of the invention pertains to nonhuman transgenic animals which contain cells carrying a transgene encoding a human MEKK protein or a portion of a human MEKK protein. In a subembodiment, of the transgenic animals of the invention, the transgene alters an endogenous gene encoding an endogenous MEKK protein (e.g., homologous recombinant animals in which the endogenous MEKK gene has been functionally disrupted or “knocked out”, or the nucleotide sequence of the endogenous MEKK gene has been mutated or the transcriptional regulatory region of the endogenous MEKK gene has been altered).

A transgenic animal of the invention can be created by introducing human MEKK-encoding nucleic acid into the male pronuclei of a fertilized oocyte, e.g., by microinjection, and allowing the oocyte to develop in a pseudopregnant female foster animal. The human MEKK nucleotide sequence of SEQ ID NO: 1 (and plasmid pHu-MEKK) can be introduced as a transgene into the genome of a non-human animal. Intronic sequences and polyadenylation signals can also be included in the transgene to increase the efficiency of expression of the transgene. A tissue-specific regulatory sequence(s) can be operably linked to the human MEKK transgene to direct expression of human MEKK protein to particular cells. Methods for generating transgenic animals via embryo manipulation and microinjection, particularly animals such as mice, have become conventional in the art and are described, for example, in U.S. Pat. Nos. 4,736,866 and 4,870,009, both by Leder et al., U.S. Pat. No. 4,873,191 by Wagner et al. and in Hogan, B., Manipulating the Mouse Embryo, (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1986). Similar methods are used for production of other transgenic animals. A transgenic founder animal can be identified based upon the presence of the human MEKK transgene in its genome and/or expression of human MEKK mRNA in tissues or cells of the animals. A transgenic founder animal can then be used to breed additional animals carrying the transgene. Moreover, transgenic animals carrying a transgene encoding human MEKK can further be bred to other transgenic animals carrying other transgenes.

To create a homologous recombinant animal, a vector is prepared which contains at least a portion of a human MEKK gene into which a deletion, addition or substitution has been introduced to thereby alter, e.g., functionally disrupt, the endogenous MEKK gene. In one embodiment, a homologous recombination vector is designed such that, upon homologous recombination, the endogenous MEKK gene is functionally disrupted (i.e., no longer encodes a functional protein; also referred to as a “knock out” vector). Alternatively, the vector can be designed such that, upon homologous recombination, the endogenous MEKK gene replaced by the human MEKK gene. In the homologous recombination vector, the altered portion of theMEKK gene is flanked at its 5′ and 3′ ends by additional nucleic acid of the MEKK gene to allow for homologous recombination to occur between the exogenous human MEKK gene carried by the vector and an endogenous MEKK gene in an embryonic stem cell. The additional flanking MEKK nucleic acid is of sufficient length for successful homologous recombination with the endogenous gene. Typically, several kilobases of flanking DNA (both at the 5′ and 3′ ends) are included in the vector (see e.g., Thomas, K. R. and Capecchi, M. R. (1987) Cell 51:503 for a description of homologous recombination vectors). The vector is introduced into an embryonic stem cell line (e.g., by electroporation) and cells in which the introduced human MEKK gene has homologously recombined with the endogenous MEKK gene are selected (see e.g., Li, E. et al. (1992) Cell 69:915). The selected cells are then injected into a blastocyst of an animal (e.g., a mouse) to form aggregation chimeras (see e.g., Bradley, A. in Teratocarcinomas and Embryonic Stem Cells: A Practical Approach, E. J. Robertson, ed. (IRL, Oxford, 1987) pp. 113-152). A chimeric embryo can then be implanted into a suitable pseudopregnant female foster animal and the embryo brought to term. Progeny harboring the homologously recombined DNA in their germ cells can be used to breed animals in which all cells of the animal contain the homologously recombined DNA by germline transmission of the transgene. Methods for constructing homologous recombination vectors and homologous recombinant animals are described further in Bradley, A. (1991) Current Opinion in Biotechnology 2:823-829 and in PCT International Publication Nos.: WO 90/11354 by Le Mouellec et al.; WO 91/01140 by Smithies et al.; WO 92/0968 by Zijlstra et al.; and WO 93/04169 by Berns et al.

In addition to the foregoing, the skilled artisan will appreciate that other approaches known in the art for homologous recombination can be applied to the instant invention. Enzyme-assisted site-specific integration systems are known in the art and can be applied to integrate a DNA molecule at a predetermined location in a second target DNA molecule. Examples of such enzyme-assisted integration systems include the Cre recombinase-lox target system (e.g., as described in Baubonis, W. and Sauer, B. (1993) Nuc. Acids Res. 21:2025-2029; and Fukushige, S. and Sauer, B. (1992) Proc. Natl. Acad. Sci. USA 89:7905-7909) and the FLP recombinase-FRT target system (e.g., as described in Dang, D. T. and Perrimon, N. (1992) Dev. Genet. 13:367-375; and Fiering, S. et al. (1993) Proc. Natl. Acad. Sci. USA 90:8469-8473). Tetracycline-regulated inducible homologous recombination systems, such as described in PCT Publication No. WO 94/29442 and PCT Publication No. WO 96/01313, also can be used.

III. Isolated Human MEKK Proteins and Anti-Human MEKK Antibodies

Another aspect of the invention pertains to isolated human MEKK proteins. Preferably, the human MEKK protein comprises the amino acid sequence of SEQ ID NO: 2. In other embodiments, the protein has at least 90-91% amino acid identity, more preferably 92-93% amino identity, more preferably 94-95% amino identity, more preferably 96-97% amino identity, more preferably 98-99% amino identity, and even more preferably 99.5% amino acid identity with the amino acid sequence of SEQ ID NO:2, SEQ ID NO:4, or SEQ ID NO:6.

In other embodiments, the invention provides isolated portions of the human MEKK protein. For example, the invention further encompasses an amino-terminal portion of human MEKK that includes a regulatory domain. This portion encompasses, for example, about amino acids 1-xxx of SEQ ID NO:2, about amino aicds 1-360 of SEQ ID NO:4, or about amino acids 1-366 of SEQ ID NO:6. Another isolated portion of human MEKK provided by the invention is a carboxy-terminal catalytic domain. This portion encompasses, for example, about amino acids 1038-1302 of SEQ ID NO:2, about amino acids 361-619 of SEQ ID NO:4, or about amino acids 367-626 of SEQ ID NO:6. In yet other embodiments, the invention provides biologically active portions of the human MEKK protein.

As used interchangeably herein, a “MEKK activity”, “biological activity of MEKK” or “functional activity of MEKK”, refers to an activity exerted by a MEKK protein, polypeptide or portion thereof as determined in vivo, or in vitro, according to standard techniques.

In one embodiment, a MEKK activity is a direct activity, such as an association with a MEKK-target molecule. As used herein, a “target molecule” is a molecule with which a MEKK protein binds or interacts in nature, such that MEKK-mediated function is acheived. A MEKK target molecule can be a non-MEKK molecule or a MEKK protein or polypeptide of the present invention (e.g., an autoactivity). In an exemplary embodiment, a MEKK target molecule is a MEKK substrate (e.g., MEK or JNKK). Alternatively, an STMST activity is an indirect activity, such as a cellular signaling activity mediated by interaction of the MEKK protein with a MEKK ligand.

In a preferred embodiment, a MEKK activity is at least one or more of the following activities: (i) interaction of a MEKK protein with soluble MEKK ligand (e.g., MEK or JNKK); (ii) modulation of the activity of a MEKK substrate; (iii) activation of a MEKK substrate; (iv) indirect modulation of a downstream signaling molecule (e.g., MAPK, for example p⁴²/p^(44MAPK) or (JNK).

In yet another preferred embodiment, a MEKK activity is at least one or more of the following activities: (1) modulation of cellular signal transduction, either in vitro or in vivo; (2) regulation of gene transcription in a cell expressing a MEKK protein; (3) regulation of gene transcription in a cell expressing a MEKK protein, wherein said cell is involved inflammation; (4) regulation of cellular proliferation; (5) regulation of cellular differentiation; (6) regulation of develpoment; (7) regulation of cell death; or (8) regulation of regulation of inflammation.

Human MEKK proteins of the invention are preferably produced by recombinant DNA techniques. For example, a nucleic acid molecule encoding the protein is cloned into an expression vector (as described above), the expression vector is introduced into a host cell (as described above) and the human MEKK protein is expressed in the host cell. The human MEKK protein can then be isolated from the cells by an appropriate purification scheme using standard protein purification techniques. Alternative to recombinant expression, a human MEKK polypeptide can be synthesized chemically using standard peptide synthesis techniques. Moreover, native human MEKK protein can be isolated from cells (e.g., from T cells), for example by immunoprecipitation using an anti-human MEKK antibody.

The invention also provides human MEKK fusion proteins. As used herein, a human MEKK “fusion protein” comprises a human MEKK polypeptide operatively linked to a polypeptide other than human MEKK. A “human MEKK polypeptide” refers to a polypeptide having an amino acid sequence corresponding to human MEKK protein, or a peptide fragment thereof which is unique to human MEKK protein (as compared to non-human MEKK proteins, such as mouse or chicken MEKK”, whereas a “polypeptide other than human MEKK” refers to a polypeptide having an amino acid sequence corresponding to another protein. Within the fusion protein, the term “operatively linked” is intended to indicate that the human MEKK polypeptide and the other polypeptide are fused in-frame to each other. The other polypeptide may be fused to the N-terminus or C-terminus of the human MEKK polypeptide. For example, in one embodiment, the fusion protein is a GST-human MEKK fusion protein in which the human MEKK sequences are fused to the C-terminus of the GST sequences. In another embodiment, the fusion protein is a human MEKK-HA fusion protein in which the human MEKK nucleotide sequence is inserted in a vector such as pCEP4-HA vector (Herrscher, R. F. et al. (1995) Genes Dev. 9:3067-3082) such that the human MEKK sequences are fused in frame to an influenza hemagglutinin epitope tag. Such fusion proteins can facilitate the purification of recombinant human MEKK.

Preferably, a human MEKK fusion protein of the invention is produced by standard recombinant DNA techniques. For example, DNA fragments coding for the different polypeptide sequences are ligated together in-frame in accordance with conventional techniques, for example employing blunt-ended or stagger-ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment, the fusion gene can be synthesized by conventional techniques including automated DNA synthesizers. Alternatively, PCR amplification of gene fragments can be carried out using anchor primers which give rise to complementary overhangs between two consecutive gene fragments which can subsequently be annealed and reamplified to generate a chimeric gene sequence (see, for example, Current Protocols in Molecular Biology, eds. Ausubel et al. John Wiley & Sons: 1992). Moreover, many expression vectors are commercially available that already encode a fusion moiety (e.g., a GST polypeptide or an HA epitope tag). A human MEKK-encoding nucleic acid can be cloned into such an expression vector such that the fusion moiety is linked in-frame to the human MEKK protein.

An isolated human MEKK protein, or fragment thereof, can be used as an immunogen to generate antibodies that bind specifically to human MEKK using standard techniques for polyclonal and monoclonal antibody preparation. The human MEKK protein can be used to generate antibodies or, alternatively, an antigenic peptide fragment of human MEKK can be used as the immunogen. An antigenic peptide fragment of human MEKK typically comprises at least 8 amino acid residues of the amino acid sequence shown in SEQ ID NO:2, SEQ ID NO:4, or SEQ ID NO:6 and encompasses an epitope of human MEKK such that an antibody raised against the peptide forms a specific immune complex with human MEKK. Preferably, the antigenic peptide comprises at least 10 amino acid residues, more preferably at least 15 amino acid residues, even more preferably at least 20 amino acid residues, and most preferably at least 30 amino acid residues. Preferred epitopes encompassed by the antigenic peptide are regions of human MEKK that are located on the surface of the protein, e.g., hydrophilic regions, and that are unique to human MEKK, as compared to MEKK proteins from other species, such as chicken or mouse (i.e., an antigenic peptide that spans a region of human MEKK that is not conserved across species is used as immunogen; such non-conserved regions/residues are underlined and bolded in FIG. 4, FIG. 8, or FIG. 12). A standard hydrophobicity analysis of the human MEKK protein can be performed to identify hydrophilic regions.

A human MEKK immunogen typically is used to prepare antibodies by immunizing a suitable subject, (e.g., rabbit, goat, mouse or other mammal) with the immunogen. An appropriate immunogenic preparation can contain, for examples, recombinantly expressed human MEKK protein or a chemically synthesized human MEKK peptide. The preparation can further include an adjuvant, such as Freund's complete or incomplete adjuvant, or similar immunostimulatory agent. Immunization of a suitable subject with an immunogenic human MEKK preparation induces a polyclonal anti-human MEKK antibody response.

Accordingly, another aspect of the invention pertains to anti-human MEKK antibodies. Polyclonal anti-human MEKK antibodies can be prepared as described above by immunizing a suitable subject with a human MEKK immunogen. The anti-human MEKK antibody titer in the immunized subject can be monitored over time by standard techniques, such as with an enzyme linked immunosorbent assay (ELISA) using immobilized human MEKK. If desired, the antibody molecules directed against human MEKK can be isolated from the mammal (e.g., from the blood) and further purified by well known techniques, such as protein A chromatography to obtain the IgG fraction. At an appropriate time after immunization, e.g., when the anti-human MEKK antibody titers are highest, antibody-producing cells can be obtained from the subject and used to prepare monoclonal antibodies by standard techniques, such as the hybridoma technique originally described by Kohler and Milstein (1975, Nature 256:495-497) (see also, Brown et al. (1981) J. Immunol 127:539-46; Brown et al. (1980) J. Biol Chem 255:4980-83; Yeh et al. (1976) PNAS 76:2927-31; and Yeh et al. (1982) Int. J. Cancer 29:269-75), the more recent human B cell hybridoma technique (Kozbor et al. (1983) Immunol Today 4:72), the EBV-hybridoma technique (Cole et al. (1985), Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96) or trioma techniques. The technology for producing monoclonal antibody hybridomas is well known (see generally R. H. Kenneth, in Monoclonal Antibodies: A New Dimension In Biological Analyses, Plenum Publishing Corp., New York, N.Y. (1980); E. A. Lerner (1981) Yale J. Biol. Med., 54:387-402; M. L. Gefter et al. (1977) Somatic Cell Genet., 3:231-36). Briefly, an immortal cell line (typically a myeloma) is fused to lymphocytes (typically splenocytes) from a mammal immunized with a human MEKK immunogen as described above, and the culture supernatants of the resulting hybridoma cells are screened to identify a hybridoma producing a monoclonal antibody that binds specifically to human MEKK.

Any of the many well known protocols used for fusing lymphocytes and immortalized cell lines can be applied for the purpose of generating an anti-human MEKK monoclonal antibody (see, e.g., G. Galfre et al. (1977) Nature 266:55052; Gefter et al. Somatic Cell Genet., cited supra; Lerner, Yale J. Biol. Med., cited supra; Kenneth, Monoclonal Antibodies, cited supra). Moreover, the ordinary skilled worker will appreciate that there are many variations of such methods which also would be useful. Typically, the immortal cell line (e.g., a myeloma cell line) is derived from the same mammalian species as the lymphocytes. For example, murine hybridomas can be made by fusing lymphocytes from a mouse immunized with an immunogenic preparation of the present invention with an immortalized mouse cell line. Preferred immortal cell lines are mouse myeloma cell lines that are sensitive to culture medium containing hypoxanthine, aminopterin and thymidine (“HAT medium”). Any of a number of myeloma cell lines may be used as a fusion partner according to standard techniques, e.g., the P3-NS1/1-Ag4-1, P3-x63-Ag8.653 or Sp2/O—Ag14 myeloma lines. These myeloma lines are available from the American Type Culture Collection (ATCC), Rockville, Md. Typically, HAT-sensitive mouse myeloma cells are fused to mouse splenocytes using polyethylene glycol (“PEG”). Hybridoma cells resulting from the fusion are then selected using HAT medium, which kills unfused and unproductively fused myeloma cells (unfused splenocytes die after several days because they are not transformed). Hybridoma cells producing a monoclonal antibody of the invention are detected by screening the hybridoma culture supernatants for antibodies that bind human MEKK, e.g., using a standard ELISA assay.

Alternative to preparing monoclonal antibody-secreting hybridomas, a monoclonal anti-human MEKK antibody can be identified and isolated by screening a recombinant combinatorial immunoglobulin library (e.g., an antibody phage display library) with human MEKK to thereby isolate immunoglobulin library members that bind human MEKK. Kits for generating and screening phage display libraries are commercially available (e.g., the Pharmacia Recombinant Phage Antibody System, Catalog No. 27-9400-01; and the Stratagene SurfZAP™ Phage Display Kit, Catalog No. 240612). Additionally, examples of methods and reagents particularly amenable for use in generating and screening antibody display library can be found in, for example, Ladner et al. U.S. Pat. No. 5,223,409; Kang et al. International Publication No. WO 92/18619; Dower et al. International Publication No. WO 91/17271; Winter et al. International Publication WO 92/20791; Markland et al. International Publication No. WO 92/15679; Breitling et al. International Publication WO 93/01288; McCafferty et al. International Publication No. WO 92/01047; Garrard et al. International Publication No. WO 92/09690; Ladner et al. International Publication No. WO 90/02809; Fuchs et al. (1991) Bio/Technology 9:1370-1372; Hay et al. (1992) Hum Antibod Hybridomas 3:81-85; Huse et al. (1989) Science 246:1275-1281; Griffiths et al. (1993) EMBO J 12:725-734; Hawkins et al. (1992) J Mol Biol 226:889-896; Clarkson et al. (1991) Nature 352:624-628; Gram et al. (1992) PNAS 89:3576-3580; Garrad et al. (1991) Bio/Technology 9:1373-1377; Hoogenboom et al. (1991) Nuc Acid Res 19:4133-4137; Barbas et al. (1991) PNAS 88:7978-7982; and McCafferty et al. Nature (1990) 348:552-554.

Additionally, recombinant anti-human MEKK antibodies, such as chimeric and humanized monoclonal antibodies, comprising both human and non-human portions, which can be made using standard recombinant DNA techniques, are within the scope of the invention. Such chimeric and humanized monoclonal antibodies can be produced by recombinant DNA techniques known in the art, for example using methods described in Robinson et al. International Patent Publication PCT/US86/02269; Akira, et al. European Patent Application 184,187; Taniguchi, M., European Patent Application 171,496; Morrison et al. European Patent Application 173,494; Neuberger et al. PCT Application WO 86/01533; Cabilly et al. U.S. Pat. No. 4,816,567; Cabilly et al. European Patent Application 125,023; Better et al. (1988) Science 240:1041-1043; Liu et al. (1987) PNAS 84:3439-3443; Liu et al. (1987) J. Immunol. 139:3521-3526; Sun et al. (1987) PNAS 84:214-218; Nishimura et al. (1987) Canc. Res. 47:999-1005; Wood et al. (1985) Nature 314:446-449; and Shaw et al. (1988) J. Natl Cancer Inst. 80:1553-1559); Morrison, S. L. (1985) Science 229:1202-1207; Oi et al. (1986) BioTechniques 4:214; Winter U.S. Pat. 5,225,539; Jones et al. (1986) Nature 321:552-525; Verhoeyan et al. (1988) Science 239:1534; and Beidler et al. (1988) J. Immunol. 141:4053-4060.

An anti-human MEKK antibody (e.g., monoclonal antibody) can be used to isolate human MEKK by standard techniques, such as affinity chromatography or immunoprecipitation. An anti-human MEKK antibody can facilitate the purification of natural human MEKK from cells and of recombinantly produced human MEKK expressed in host cells. Moreover, an anti-human MEKK antibody can be used to detect human MEKK protein (e.g., in a cellular lysate or cell supernatant). Detection may be facilitated by coupling (i.e., physically linking) the antibody to a detectable substance. Accordingly, in one embodiment, an anti-human MEKK antibody of the invention is labeled with a detectable substance. Examples of detectable substances include various enzymes, prosthetic groups, fluorescent materials, luminescent materials and radioactive materials. Examples of suitable enzymes include horseradish peroxidase, alkaline phosphatase, β-galactosidase, or acetylcholinesterase; examples of suitable prosthetic group complexes include streptavidin/biotin and avidin/biotin; examples of suitable fluorescent materials include umbelliferone, fluorescein, fluorescein isothiocyanate, rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride or phycoerythrin; an example of a luminescent material includes luminol; and examples of suitable radioactive material include ¹²⁵I, ¹³II, ³⁵S or ³H.

Yet another aspect of the invention pertains to anti-human MEKK antibodies that are obtainable by a process comprising:

(a) immunizing an animal with an immunogenic human MEKK protein, or an immunogenic portion thereof unique to human MEKK protein; and

(b) isolating from the animal antibodies that specifically bind to a human MEKK protein.

Methods for immunization and recovery of the specific anti-human MEKK antibodies are described further above.

IV. Pharmaceutical Compositions

Human MEKK modulators of the invention (e.g., human MEKK inhibitory or stimulatory agents, including human MEKK proteins and antibodies) can be incorporated into pharmaceutical compositions suitable for administration. Such compositions typically comprise the modulatory agent and a pharmaceutically acceptable carrier. As used herein the term “pharmaceutically acceptable carrier” is intended to include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the compositions is contemplated. Supplementary active compounds can also be incorporated into the compositions.

A pharmaceutical composition of the invention is formulated to be compatible with its intended route of administration. For example, solutions or suspensions used for parenteral, intradermal, or subcutaneous application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic.

Pharmaceutical compositions suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. For intravenous administration, suitable carriers include physiological saline, bacteriostatic water, Cremophor EL™ (BASF, Parsippany, N.J.) or phosphate buffered saline (PBS). In all cases, the composition must be sterile and should be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyetheylene glycol, and the like), and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. Prevention of the action of microorganisms can be achieved by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, polyalcohols such as manitol, sorbitol, sodium chloride in the composition. Prolonged absorption of the injectable compositions can be brought about by including in the composition an agent which delays absorption, for example, aluminum monostearate and gelatin.

Sterile injectable solutions can be prepared by incorporating the active compound in the required amount in an appropriate solvent with one or a combination of ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the active compound into a sterile vehicle which contains a basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and freeze-drying which yields a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof.

Oral compositions generally include an inert diluent or an edible carrier. They can be enclosed in gelatin capsules or compressed into tablets. For the purpose of oral therapeutic administration, the active compound can be incorporated with excipients and used in the form of tablets, troches, or capsules. Oral compositions can also be prepared using a fluid carrier for use as a mouthwash, wherein the compound in the fluid carrier is applied orally and swished and expectorated or swallowed. Pharmaceutically compatible binding agents, and/or adjuvant materials can be included as part of the composition. The tablets, pills, capsules, troches and the like can contain any of the following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate or Sterotes; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin; or a flavoring agent such as peppermint, methyl salicylate, or orange flavoring.

In one embodiment, the active compounds are prepared with carriers that will protect the compound against rapid elimination from the body, such as a controlled release formulation, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Corporation and Nova Pharmaceuticals, Inc. Liposomal suspensions (including liposomes targeted to infected cells with monoclonal antibodies to viral antigens) can also be used as pharmaceutically acceptable carriers. These may be prepared according to methods known to those skilled in the art, for example, as described in U.S. Pat. No. 4,522,811.

V. Methods of the Invention

A. Detection Assays

Another aspect of the invention pertains to methods of using the various human MEKK compositions of the invention. For example, the invention provides a method for detecting the presence of human MEKK activity in a biological sample. The method involves contacting the biological sample with an agent capable of detecting human MEKK activity, such as human MEKK protein or human MEKK mRNA, such that the presence of human MEKK activity is detected in the biological sample.

A preferred agent for detecting human MEKK mRNA is a labeled nucleic acid probe capable of specifically hybridizing to human MEKK mRNA. The nucleic acid probe can be, for example, the human MEKK DNA of SEQ ID NO:1, SEQ ID NO:3, or SEQ ID NO:5 (or plasmid pHu-MEKK1, plasmid pHu-MEKK2, or plasmid pHu-MEKK3), or a portion thereof unique to human MEKK (as compared to MEKK from other species, such as chicken or mouse), such as an oligonucleotide of at least 15, 30, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1000 nucleotides in length and sufficient to specifically hybridize under stringent conditions to human MEKK mRNA.

A preferred agent for detecting human MEKK protein is a labeled antibody capable of binding to human MEKK protein. Antibodies can be polyclonal, or more preferably, monoclonal. An intact antibody, or a fragment thereof (e.g., Fab or F(ab′)₂) can be used. The term “labeled”, with regard to the probe or antibody, is intended to encompass direct labeling of the probe or antibody by coupling (i.e., physically linking) a detectable substance to the probe or antibody, as well as indirect labeling of the probe or antibody by reactivity with another reagent that is directly labeled. Examples of indirect labeling include detection of a primary antibody using a fluorescently labeled secondary antibody and end-labeling of a DNA probe with biotin such that it can be detected with fluorescently labeled streptavidin. The term “biological sample” is intended to include tissues, cells and biological fluids. For example, techniques for detection of human MEKK mRNA include Northern hybridizations and in situ hybridizations. Techniques for detection of human MEKK protein include enzyme linked immunosorbent assays (ELISAs), Western blots, immunoprecipitations and immunofluorescence.

B. Screening Assays

The invention provides a method (also referred to herein as a “screening assay”) for identifying modulators, i.e., candidate or test compounds or agents (e.g., peptides, peptidomimetics, small molecules or other drugs) which bind to MEKK proteins, have a stimulatory or inhibitory effect on, for example, MEKK expression or MEKK activity, or have a stimulatory or inhibitory effect on, for example, the activity of an MEKK target molecule.

In one embodiment, the invention provides assays for screening candidate or test compounds which bind to or interact with a MEKK protein or polypeptide or biologically active portion thereof. In another embodiment, the invention provides assays for screening candidate or test compounds which bind to or modulate the activity of a MEKK protein or polypeptide or biologically active portion thereof. The test compounds of the present invention can be obtained using any of the numerous approaches in combinatorial library methods known in the art, including: biological libraries; spatially addressable parallel solid phase or solution phase libraries; synthetic library methods requiring deconvolution; the ‘one-bead one-compound’ library method; and synthetic library methods using affinity chromatography selection. The biological library approach is limited to peptide libraries, while the other four approaches are applicable to peptide, non-peptide oligomer or small molecule libraries of compounds (Lam, K. S. (1997) Anticancer Drug Des. 12:145).

Examples of methods for the synthesis of molecular libraries can be found in the art, for example in: DeWitt et al. (1993) Proc. Natl. Acad. Sci. U.S.A. 90:6909; Erb et al. (1994) Proc. Natl. Acad. Sci. USA 91:11422; Zuckermann et al. (1994). J. Med. Chem. 37:2678; Cho et al. (1993) Science 261:1303; Carrell et al. (1994) Angew. Chem. Int. Ed. Engl. 33:2059; Carell et al. (1994) Angew. Chem. Int. Ed. Engl. 33:2061; and in Gallop et al. (1994) J. Med. Chem. 37:1233.

Libraries of compounds may be presented in solution (e.g., Houghten (1992) Biotechniques 13:412-421), or on beads (Lam (1991) Nature 354:82-84), chips (Fodor (1993) Nature 364:555-556), bacteria (Ladner U.S. Pat. No. 5,223,409), spores (Ladner U.S. Pat. No. '409), plasmids (Cull et al. (1992) Proc Natl Acad Sci USA 89:1865-1869) or on phage (Scott and Smith (1990) Science 249:386-390); (Devlin (1990) Science 249:404-406); (Cwirla et al. (1990) Proc. Natl. Acad. Sci. 87:6378-6382); (Felici (1991) J. Mol. Biol. 222:301-310); (Ladner supra.).

In one embodiment, an assay is a cell-free assay for identifying compounds which bind to or interact with a MEKK protein of the present invention. For example, the invention provides a method for identifying a compound that binds to or interacts with a human MEKK protein, comprising

providing an indicator composition that comprises a human MEKK protein, or biologically active portion thereof;

contacting the indicator composition with a test compound; and

determining the ability of the test compound to bind to or interact with the human MEKK protein or biologically active portion thereof in the indicator composition to thereby identify a compound that binds to or interacts with a human MEKK protein.

Determining the ability of the test compound to bind to or interact with the MEKK protein or biologically active potion thereof can be accomplished, for example, by coupling either the test compound or the MEKK protein or biologically active portion thereof with a radioisotope or enzymatic label such that binding can be determined by detecting the labeled test compound or MEKK protein or biologically active portion thereof in a complex. For example, compounds (e.g., MEKK protein or biologically active portion thereof) can be labeled with ¹²⁵I, ³⁵S, ¹⁴C, or ³H, either directly or indirectly, and the radioisotope detected by direct counting of radioemmission or by scintillation counting. Alternatively, compounds can be enzymatically labeled with, for example, horseradish peroxidase, alkaline phosphatase, or luciferase, and the enzymatic label detected by determination of conversion of an appropriate substrate to product.

Determining the ability of the test compound to bind to a MEKK protein or biologically active portion thereof can also be accomplished using a technology such as real-time Biomolecular Interaction Analysis (BIA). Sjolander, S. and Urbaniczky, C. (1991) Anal. Chem. 63:2338-2345 and Szabo et al. (1995) Curr. Opin. Struct. Biol. 5:699-705. As used herein, “BIA” is a technology for studying biospecific interactions in real time, without labeling any of the interactants (e.g., BIAcore). Changes in the optical phenomenon of surface plasmon resonance (SPR) can be used as an indication of real-time reactions between biological molecules.

In another embodiment, an assay of the present invention the invention provides a method for identifying a compound that modulates the activity of a human MEKK protein, comprising

providing an indicator composition that comprises a human MEKK protein, or biologically active portion thereof;

contacting the indicator composition with a test compound; and

determining the effect of the test compound on the activity of the human MEKK protein or biologically active portion thereof, in the indicator composition to thereby identify a compound that modulates the activity of a human MEKK protein.

Determining the effect of the test compound on the activity of the human MEKK protein can be accomplished directly by detecting a biological activity of the MEKK protein or portion thereof. Alternatively, determining the effect of the test compound on the activity of the human MEKK protein can be accomplished by detecting activity of a downstream target of MEKK, e.g., induction of a cellular second messenger of the target (i.e. intracellular Ca²⁺, diacylglycerol, IP₃, etc.), catalytic/enzymatic activity of the target an appropriate substrate, detecting the induction of a reporter gene (comprising a target-responsive regulatory element operatively linked to a nucleic acid encoding a detectable marker, e.g., luciferase), or detecting a target-regulated cellular response, for example, DNA:protein or protein:protein interactions.

In another embodiment, a screening assay of the invention is a cell based assay. For example, the indicator composition can comprise an indicator cell (e.g., a mammalain cell or a yeast cell), wherein said indicator cell comprises: (i) the a human MEKK protein or biologically active portion thereof. Preferably, the indicator cell contains:

-   -   i) a recombinant expression vector encoding the human MEKK; and         said method comprises:

a) contacting the indicator cell with a test compound;

b) determining the effect of the test compound on the activity of the MEKK protein or biologically active portion thereof to thereby identify a compound that modulates the activity of human MEKK.

In another embodiment, the assay further comprises the step of

c) comparing the activity of the MEKK protein or biologically active portion thereof in the indicator cell in the presence of the test compound with the activity of the MEKK protein or biologically active portion thereof in the indicator cell in the absence of the test compound to thereby identify a compound that modulates the activity of human MEKK.

In another example, the indicator composition can comprise an indicator cell, wherein said indicator cell comprises: (i) the a human MEKK protein or biologically active portion thereof and (ii) a reporter gene responsive to the human MEKK protein. Preferably, the indicator cell contains:

-   -   i) a recombinant expression vector encoding the human MEKK; and     -   ii) a vector comprising regulatory sequences of a gene         responsive to MEKK signal transduction (e,g, a gene containing         regulatory sequences responsive to the transcription factor,         ATF 2) operatively linked to a reporter gene; and said method         comprises:

a) contacting the indicator cell with a test compound;

b) determining the level of expression of the reporter gene in the indicator cell in the presence of the test compound to thereby identify a compound that modulates the activity of human MEKK.

In another embodiment, the assay further comprises the step of

c) comparing the level of expression of the reporter gene in the indicator cell in the presence of the test compound with the level of expression of the reporter gene in the indicator cell in the absence of the test compound to thereby identify a compound that modulates the activity of human MEKK.

In another preferred embodiment, the indicator composition comprises a preparation of: (i) a human MEKK protein and (ii) a DNA molecule to which an ATF 2 transcription factor binds, and

said method comprises:

a) contacting the indicator composition with a test compound;

b) determining the degree of interaction of an ATF 2 transcription factor and the DNA molecule in the presence of the test compound; and

c) comparing the degree of interaction of ATF 2 transcription factor and the DNA molecule in the presence of the test compound with the degree of interaction of the ATF 2 transcription factor and the DNA molecule in the absence of the test compound to thereby identify a compound that modulates the activity of human MEKK.

In another preferred embodiment, the method identifies proteins that interact with human MEKK. In this embodiment,

the indicator composition is an indicator cell, which indicator cell comprises:

-   -   i) a reporter gene operably linked to a transcriptional         regulatory sequence; and     -   ii) a first chimeric gene which encodes a first fusion protein,         said first fusion protein including human MEKK;

the test compound comprises a library of second chimeric genes, which library encodes second fusion proteins;

expression of the reporter gene being sensitive to interactions between the first fusion protein, the second fusion protein and the transcriptional regulatory sequence; and

wherein the effect of the test compound on human MEKK in the indicator composition is determined by detecting the level of expression of the reporter gene in the indicator cell to thereby identify a test compound comprising a protein that interacts with human MEKK.

Furthermore, the present invention provides assays comprising the step of contacting an indicator composition with a compound which is known to interact with, bind to, or modulate the activity of a MEKK protein or biologically active portion thereof and determining the ability of a test compound to effect the ability of the known compound to bind to, interact with, or modulate the activity of the MEKK protein or biologically active portion thereof.

Recombinant expression vectors that can be used for expression of human MEKK in the indicator cell are known in the art (see discussions above). In one embodiment, within the expression vector the human MEKK-coding sequences are operatively linked to regulatory sequences that allow for constitutive expression of human MEKK in the indicator cell (e.g., viral regulatory sequences, such as a cytomegalovirus promoter/enhancer, can be used). Use of a recombinant expression vector that allows for constitutive expression of human MEKK in the indicator cell is preferred for identification of compounds that enhance or inhibit the activity of human MEKK. In an alternative embodiment, within the expression vector the human MEKK-coding sequences are operatively linked to regulatory sequences of the endogenous human MEKK gene (i.e., the promoter regulatory region derived from the endogenous human MEKK gene). Use of a recombinant expression vector in which human MEKK expression is controlled by the endogenous regulatory sequences is preferred for identification of compounds that enhance or inhibit the transcriptional expression of human MEKK.

A variety of reporter genes are known in the art and are suitable for use in the screening assays of the invention. Examples of suitable reporter genes include those which encode chloramphenicol acetyltransferase, beta-galactosidase, alkaline phosphatase or luciferase. Standard methods for measuring the activity of these gene products are known in the art. Likewise, a variety of cell types are suitable for use as an indicator cell in the screening assay. Preferably a cell line is used which does not normally express human MEKK. Mammalian cell lines as well as yeast cells can be used as indicator cells.

In one embodiment, the level of expression of the reporter gene in the indicator cell in the presence of the test compound is higher than the level of expression of the reporter gene in the indicator cell in the absence of the test compound and the test compound is identified as a compound that stimulates the expression or activity of human MEKK. In another embodiment, the level of expression of the reporter gene in the indicator cell in the presence of the test compound is lower than the level of expression of the reporter gene in the indicator cell in the absence of the test compound and the test compound is identified as a compound that inhibits the expression or activity of human MEKK.

Alternative to the use of a reporter gene construct, compounds that modulate the expression or activity of human MEKK can be identified by using other “read-outs.” For example, an indicator cell can be transfected with a human MEKK expression vector, incubated in the presence and in the absence of a test compound, and MEKK activity be assessed by detecting the mRNA of an ATF 2-responsive gene product. Standard methods for detecting mRNA, such as reverse transcription-polymerase chain reaction (RT-PCR) are known in the art. Alternatively, MEKK activity can be assesed by detecting ATF2 mRNA levels.

As described above, the invention provides a screening assay for identifying proteins that interact with human MEKK. These assays can be designed based on the two-hybrid assay system (also referred to as an interaction trap assay) known in the art (see e.g., Field U.S. Pat. No. 5,283,173; Zervos et al. (1993) Cell 72:223-232; Madura et al. (1993) J. Biol. Chem. 268:12046-12054; Bartel et al. (1993) Biotechniques 14:920-924; and Iwabuchi et al. (1993) Oncogene 8:1693-1696). The two-hybrid assay is generally used for identifying proteins that interact with a particular target protein. The assay employs gene fusions to identify proteins capable of interacting to reconstitute a functional transcriptional activator. The transcriptional activator consists of a DNA-binding domain and a transcriptional activation domain, wherein both domains are required to activate transcription of genes downstream from a target sequence (such as an upstream activator sequence (UAS) for GAL4). DNA sequences encoding a target “bait” protein are fused to either of these domains and a library of DNA sequences is fused to the other domain. “Fish” fusion proteins (generated from the fusion library) capable of binding to the target-fusion protein (e.g., a target GAL4-fusion “bait”) will generally bring the two domains (DNA-binding domain and transcriptional activation domain) into close enough proximity to activate the transcription of a reporter gene inserted downstream from the target sequence. Thus, the “fish” proteins can be identified by their ability to reconstitute a functional transcriptional activator (e.g., a functional GAL4 transactivator).

This general two-hybrid system can be applied to the identification of proteins in cells that interact with human MEKK by construction of a target human MEKK fusion protein (e.g., a human MEKK/GAL4 binding domain fusion as the “bait”) and a cDNA library of “fish” fusion proteins (e.g., a cDNA/GAL4 activation domain library), wherein the cDNA library is prepared from mRNA of a cell type of interest, and introducing these constructs into a host cell that also contains a reporter gene construct linked to a regulatory sequence responsive to human MEKK. cDNAs encoding proteins that interact with human MEKK can be identified based upon transactivation of the reporter gene construct.

Alternatively, a “single-hybrid” assay, such as that described in Sieweke, M. H. et al. (1996) Cell 85:49-60, can be used to identify proteins that interact with human MEKK. This assay is a modification of the two-hybrid system discussed above. In this system, the “bait” is a transcription factor from which the transactivation domain has been removed (e.g., human MEKK from which the amino-terminal transactivation domain has been removed) and the “fish” is a non-fusion cDNA library (e.g., a cDNA library prepared from Th2 cells). These constructs are introduced into host cells (e.g., yeast cells) that also contains a reporter gene construct linked to a regulatory sequence responsive to human MEKK. cDNAs encoding proteins that interact with human MEKK can be identified based upon transactivation of the reporter gene construct.

As described above, the invention provides a screening assay for identifying compounds that modulate the activity of human MEKK by assessing the interaction between ATF 2 and a regulatory element of an ATF 2-responsive gene. Assays are known in the art that detect the interaction of a DNA binding protein with a target DNA sequence (e.g., electrophoretic mobility shift assays, DNAse I footprinting assays and the like). By performing such assays in the presence and absence of test compounds, these assays can be used to identify compounds that modulate (e.g., inhibit or enhance) the interaction of the DNA binding protein with its target DNA sequence.

In one embodiment, the amount of binding of ATF 2 to the DNA fragment in the presence of the test compound is greater than the amount of binding of ATF 2 to the DNA fragment in the absence of the test compound, in which case the test compound is identified as a compound that enhances activity of human MEKK. In another embodiment, the amount of binding of ATF 2 to the DNA fragment in the presence of the test compound is less than the amount of binding of ATF 2 to the DNA fragment in the absence of the test compound, in which case the test compound is identified as a compound that inhibits activity of human MEKK.

Yet another aspect of the invention pertains to methods of modulating human MEKK activity in a cell. The modulatory methods of the invention involve contacting the cell with an agent that modulates human MEKK activity such that human MEKK activity in the cell is modulated. The agent may act by modulating the activity of human MEKK protein in the cell or by modulating transcription of the human MEKK gene or translation of the human MEKK mRNA. As used herein, the term “modulating” is intended to include inhibiting or decreasing human MEKK activity and stimulating or increasing human MEKK activity. Accordingly, in one embodiment, the agent inhibits human MEKK activity. In another embodiment, the agent stimulates human MEKK activity.

A. Inhibitory Agents

According to a modulatory method of the invention, human MEKK activity is inhibited in a cell by contacting the cell with an inhibitory agent. Inhibitory agents of the invention can be, for example, intracellular binding molecules that act to inhibit the expression or activity of human MEKK. As used herein, the term “intracellular binding molecule” is intended to include molecules that act intracellularly to inhibit the expression or activity of a protein by binding to the protein itself, to a nucleic acid (e.g., an mRNA molecule) that encodes the protein or to a target with which the protein indirectly interacts (e.g., to a DNA target sequence to which ATF 2 binds). Examples of intracellular binding molecules, described in further detail below, include antisense human MEKK nucleic acid molecules (e.g., to inhibit translation of human MEKK mRNA), intracellular anti-human MEKK antibodies (e.g., to inhibit the activity of human MEKK protein) and dominant negative mutants of the human MEKK protein.

In one embodiment, an inhibitory agent of the invention is an antisense nucleic acid molecule that is complementary to a gene encoding human MEKK or to a portion of said gene, or a recombinant expression vector encoding said antisense nucleic acid molecule. The use of antisense nucleic acids to downregulate the expression of a particular protein in a cell is well known in the art (see e.g., Weintraub, H. et al., Antisense RNA as a molecular tool for genetic analysis, Reviews-Trends in Genetics, Vol. 1(1) 1986; Askari, F. K. and McDonnell, W. M. (1996) N. Eng. J. Med. 334:316-318; Bennett, M. R. and Schwartz, S. M. (1995) Circulation 92:1981-1993; Mercola, D. and Cohen, J. S. (1995) Cancer Gene Ther. 2:47-59; Rossi, J. J. (1995) Br. Med. Bull. 51:217-225; Wagner, R. W. (1994) Nature 372:333-335). An antisense nucleic acid molecule comprises a nucleotide sequence that is complementary to the coding strand of another nucleic acid molecule (e.g., an mRNA sequence) and accordingly is capable of hydrogen bonding to the coding strand of the other nucleic acid molecule. Antisense sequences complementary to a sequence of an mRNA can be complementary to a sequence found in the coding region of the mRNA, the 5′ or 3′ untranslated region of the mRNA or a region bridging the coding region and an untranslated region (e.g., at the junction of the 5′ untranslated region and the coding region). Furthermore, an antisense nucleic acid can be complementary in sequence to a regulatory region of the gene encoding the mRNA, for instance a transcription initiation sequence or regulatory element. Preferably, an antisense nucleic acid is designed so as to be complementary to a region preceding or spanning the initiation codon on the coding strand or in the 3′ untranslated region of an mRNA. An antisense nucleic acid for inhibiting the expression of human MEKK protein in a cell can be designed based upon the nucleotide sequence encoding the human MEKK protein (e.g., SEQ ID NO: 1), constructed according to the rules of Watson and Crick base pairing.

An antisense nucleic acid can exist in a variety of different forms. For example, the antisense nucleic acid can be an oligonucleotide that is complementary to only a portion of a human MEKK gene. An antisense oligonucleotides can be constructed using chemical synthesis procedures known in the art. An antisense oligonucleotide can be chemically synthesized using naturally occurring nucleotides or variously modified nucleotides designed to increase the biological stability of the molecules or to increase the physical stability of the duplex formed between the antisense and sense nucleic acids, e.g. phosphorothioate derivatives and acridine substituted nucleotides can be used. To inhibit human MEKK expression in cells in culture, one or more antisense oligonucleotides can be added to cells in culture media, typically at about 200 μg oligonucleotide/ml.

Alternatively, an antisense nucleic acid can be produced biologically using an expression vector into which a nucleic acid has been subcloned in an antisense orientation (i.e., nucleic acid transcribed from the inserted nucleic acid will be of an antisense orientation to a target nucleic acid of interest). Regulatory sequences operatively linked to a nucleic acid cloned in the antisense orientation can be chosen which direct the expression of the antisense RNA molecule in a cell of interest, for instance promoters and/or enhancers or other regulatory sequences can be chosen which direct constitutive, tissue specific or inducible expression of antisense RNA. For example, for inducible expression of antisense RNA, an inducible eukaryotic regulatory system, such as the Tet system (e.g., as described in Gossen, M. and Bujard, H. (1992) Proc. Natl. Acad. Sci. USA 89:5547-5551; Gossen, M. et al. (1995) Science 268:1766-1769; PCT Publication No. WO 94/29442; and PCT Publication No. WO 96/01313) can be used. The antisense expression vector is prepared as described above for recombinant expression vectors, except that the cDNA (or portion thereof) is cloned into the vector in the antisense orientation. The antisense expression vector can be in the form of, for example, a recombinant plasmid, phagemid or attenuated virus. The antisense expression vector is introduced into cells using a standard transfection technique, as described above for recombinant expression vectors.

In another embodiment, an antisense nucleic acid for use as an inhibitory agent is a ribozyme. Ribozymes are catalytic RNA molecules with ribonuclease activity which are capable of cleaving a single-stranded nucleic acid, such as an mRNA, to which they have a complementary region (for reviews on ribozymes see e.g., Ohkawa, J. et al. (1995) J. Biochem. 118:251-258; Sigurdsson, S. T. and Eckstein, F. (1995) Trends Biotechnol. 13:286-289; Rossi, J. J. (1995) Trends Biotechnol. 13:301-306; Kiehntopf, M. et al. (1995) J. Mol. Med. 73:65-71). A ribozyme having specificity for human MEKK mRNA can be designed based upon the nucleotide sequence of the human MEKK cDNA. For example, a derivative of a Tetrahymena L-19 IVS RNA can be constructed in which the base sequence of the active site is complementary to the base sequence to be cleaved in a human MEKK mRNA. See for example U.S. Pat. Nos. 4,987,071 and 5,116,742, both by Cech et al. Alternatively, human MEKK mRNA can be used to select a catalytic RNA having a specific ribonuclease activity from a pool of RNA molecules. See for example Bartel, D. and Szostak, J. W. (1993) Science 261: 1411-1418.

Another type of inhibitory agent that can be used to inhibit the expression and/or activity of human MEKK in a cell is an intracellular antibody specific for the human MEKK protein. The use of intracellular antibodies to inhibit protein function in a cell is known in the art (see e.g., Carlson, J. R. (1988) Mol. Cell. Biol. 8:2638-2646; Biocca, S. et al. (1990) EMBO J. 9:101-108; Werge, T. M. et al. (1990) FEBS Letters 274:193-198; Carlson, J. R. (1993) Proc. Natl. Acad. Sci. USA 90:7427-7428; Marasco, W. A. et al. (1993) Proc. Natl. Acad. Sci. USA 90:7889-7893; Biocca, S. et al. (1994) Bio/Technology 12:396-399; Chen, S-Y. et al. (1994) Human Gene Therapy 5:595-601; Duan, L et al. (1994) Proc. Natl. Acad. Sci. USA 91:5075-5079; Chen, S-Y. et al. (1994) Proc. Natl. Acad. Sci. USA 91:5932-5936; Beerli, R. R. et al. (1994) J. Biol. Chem. 269:23931-23936; Beerli, R. R. et al. (1994) Biochem. Biophys. Res. Commun. 204:666-672; Mhashilkar, A. M. et al. (1995) EMBO J. 14:1542-1551; Richardson, J. H. et al. (1995) Proc. Natl. Acad. Sci. USA 92:3137-3141; PCT Publication No. WO 94/02610 by Marasco et al.; and PCT Publication No. WO 95/03832 by Duan et al.).

To inhibit protein activity using an intracellular antibody, a recombinant expression vector is prepared which encodes the antibody chains in a form such that, upon introduction of the vector into a cell, the antibody chains are expressed as a functional antibody in an intracellular compartment of the cell. For inhibition of human MEKK activity according to the inhibitory methods of the invention, an intracellular antibody that specifically binds the human MEKK protein is expressed in the cytoplasm of the cell. To prepare an intracellular antibody expression vector, antibody light and heavy chain cDNAs encoding antibody chains specific for the target protein of interest, e.g., human MEKK, are isolated, typically from a hybridoma that secretes a monoclonal antibody specific for the human MEKK protein. Hybridomas secreting anti-human MEKK monoclonal antibodies, or recombinant anti-human MEKK monoclonal antibodies, can be prepared as described above. Once a monoclonal antibody specific for human MEKK protein has been identified (e.g., either a hybridoma-derived monoclonal antibody or a recombinant antibody from a combinatorial library), DNAs encoding the light and heavy chains of the monoclonal antibody are isolated by standard molecular biology techniques. For hybridoma derived antibodies, light and heavy chain cDNAs can be obtained, for example, by PCR amplification or cDNA library screening. For recombinant antibodies, such as from a phage display library, cDNA encoding the light and heavy chains can be recovered from the display package (e.g., phage) isolated during the library screening process. Nucleotide sequences of antibody light and heavy chain genes from which PCR primers or cDNA library probes can be prepared are known in the art. For example, many such sequences are disclosed in Kabat, E. A., et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242 and in the “Vbase” human germline sequence database.

Once obtained, the antibody light and heavy chain sequences are cloned into a recombinant expression vector using standard methods. To allow for cytoplasmic expression of the light and heavy chains, the nucleotide sequences encoding the hydrophobic leaders of the light and heavy chains are removed. An intracellular antibody expression vector can encode an intracellular antibody in one of several different forms. For example, in one embodiment, the vector encodes full-length antibody light and heavy chains such that a full-length antibody is expressed intracellularly. In another embodiment, the vector encodes a full-length light chain but only the VH/CH1 region of the heavy chain such that a Fab fragment is expressed intracellularly. In the most preferred embodiment, the vector encodes a single chain antibody (scFv) wherein the variable regions of the light and heavy chains are linked by a flexible peptide linker (e.g., (Gly₄Ser)₃) and expressed as a single chain molecule. To inhibit human MEKK activity in a cell, the expression vector encoding the anti-human MEKK intracellular antibody is introduced into the cell by standard transfection methods, as discussed hereinbefore.

Yet another form of an inhibitory agent of the invention is an inhibitory form of human MEKK, also referred to herein as a dominant negative inhibitor. The MEKK proteins are known to modulate the activity of MEKK target molecules, particularly by modulating the phosphorylation state of the MEKK target molecule. One means to inhibit the activity of molecule that has an enzymatic activity is through the use of a dominant negative inhibitor that has the ability to interact with the target molecule but that lacks enzymatic activity. By interacting with the target molecule, such dominant negative inhibitors can inhibit the activation of the target molecule. This process may occur naturally as a means to regulate enzymatic activity of a cellular signal transduction molecule.

Accordingly, an inhibitory agent of the invention can be a form of a human MEKK protein that has the ability to interact with other proteins but that lacks enzymatic activity. This dominant negative form of a human MEKK protein may be, for example, a mutated form of human MEKK in which a kinase consensus sequence has been altered. Such dominant negative human MEKK proteins can be expressed in cells using a recombinant expression vector encoding the human MEKK protein, which is introduced into the cell by standard transfection methods. The mutated DNA is inserted into a recombinant expression vector, which is then introduced into a cell to allow for expression of the mutated human MEKK, lacking enzymatic activity.

Other inhibitory agents that can be used to inhibit the activity of a human MEKK protein are chemical compounds that directly inhibit human MEKK activity or inhibit the interaction between human MEKK and target molecules. Such compounds can be identified using screening assays that select for such compounds, as described in detail above.

B. Stimulatory Agents

According to a modulatory method of the invention, human MEKK activity is stimulated in a cell by contacting the cell with a stimulatory agent. Examples of such stimulatory agents include active human MEKK protein and nucleic acid molecules encoding human MEKK that are introduced into the cell to increase human MEKK activity in the cell. A preferred stimulatory agent is a nucleic acid molecule encoding a human MEKK protein, wherein the nucleic acid molecule is introduced into the cell in a form suitable for expression of the active human MEKK protein in the cell. To express a human MEKK protein in a cell, typically a human MEKK-encoding DNA is first introduced into a recombinant expression vector using standard molecular biology techniques, as described herein. A human MEKK-encoding DNA can be obtained, for example, by amplification using the polymerase chain reaction (PCR), using primers based on the human MEKK nucleotide sequence. Following isolation or amplification of human MEKK-encoding DNA, the DNA fragment is introduced into an expression vector and transfected into target cells by standard methods, as described herein.

Other stimulatory agents that can be used to stimulate the activity of a human MEKK protein are chemical compounds that stimulate human MEKK activity in cells, such as compounds that directly stimulate human MEKK protein and compounds that promote the interaction between human MEKK and target molecules. Such compounds can be identified using screening assays that select for such compounds, as described in detail above.

The modulatory methods of the invention can be performed in vitro (e.g., by culturing the cell with the agent or by introducing the agent into cells in culture) or, alternatively, in vivo (e.g., by administering the agent to a subject or by introducing the agent into cells of a subject, such as by gene therapy). For practicing the modulatory method in vitro, cells can be obtained from a subject by standard methods and incubated (i.e., cultured) in vitro with a modulatory agent of the invention to modulate human MEKK activity in the cells. For example, peripheral blood mononuclear cells (PBMCs) can be obtained from a subject and isolated by density gradient centrifugation, e.g., with Ficoll/Hypaque. Specific cell populations can be depleted or enriched using standard methods. For example, monocytes/macrophages can be isolated by adherence on plastic. B cells can be enriched for example, by positive selection using antibodies to B cell surface markers, for example by incubating cells with a specific primary monoclonal antibody (mAb), followed by isolation of cells that bind the mAb using magnetic beads coated with a secondary antibody that binds the primary mAb. Specific cell populations can also be isolated by fluorescence activated cell sorting according to standard methods. If desired, cells treated in vitro with a modulatory agent of the invention can be readministered to the subject. For administration to a subject, it may be preferable to first remove residual agents in the culture from the cells before administering them to the subject. This can be done for example by a Ficoll/Hypaque gradient centrifugation of the cells. For further discussion of ex vivo genetic modification of cells followed by readministration to a subject, see also U.S. Pat. No. 5,399,346 by W. F. Anderson et al. For practicing the modulatory method in vivo in a subject, the modulatory agent can be administered to the subject such that human MEKK activity in cells of the subject is modulated. The term “subject” is intended to include living organisms in which a MEKK-dependent cellular response can be elicited. Preferred subjects are mammals. Examples of subjects include humans, monkeys, dogs, cats, mice, rats, cows, horses, goats and sheep.

For stimulatory or inhibitory agents that comprise nucleic acids (including recombinant expression vectors encoding human MEKK protein, antisense RNA, intracellular antibodies or dominant negative inhibitors), the agents can be introduced into cells of the subject using methods known in the art for introducing nucleic acid (e.g., DNA) into cells in vivo. Examples of such methods encompass both non-viral and viral methods, including:

Direct Injection: Naked DNA can be introduced into cells in vivo by directly injecting the DNA into the cells (see e.g., Acsadi et al. (1991) Nature 332:815-818; Wolff et al. (1990) Science 247:1465-1468). For example, a delivery apparatus (e.g., a “gene gun”) for injecting DNA into cells in vivo can be used. Such an apparatus is commercially available (e.g., from BioRad).

Cationic Lipids: Naked DNA can be introduced into cells in vivo by complexing the DNA with cationic lipids or encapsulating the DNA in cationic liposomes. Examples of suitable cationic lipid formulations include N-[-1-(2,3-dioleoyloxy)propyl]N,N,N-triethylammonium chloride (DOTMA) and a 1:1 molar ratio of 1,2-dimyristyloxy-propyl-3-dimethylhydroxyethylammonium bromide (DMRIE) and dioleoyl phosphatidylethanolamine (DOPE) (see e.g., Logan, J. J. et al. (1995) Gene Therapy 2:38-49; San, H. et al. (1993) Human Gene Therapy 4:781-788).

Receptor-Mediated DNA Uptake: Naked DNA can also be introduced into cells in vivo by complexing the DNA to a cation, such as polylysine, which is coupled to a ligand for a cell-surface receptor (see for example Wu, G. and Wu, C. H. (1988) J. Biol. Chem. 263:14621; Wilson et al. (1992) J. Biol. Chem. 267:963-967; and U.S. Pat. No. 5,166,320). Binding of the DNA-ligand complex to the receptor facilitates uptake of the DNA by receptor-mediated endocytosis. A DNA-ligand complex linked to adenovirus capsids which naturally disrupt endosomes, thereby releasing material into the cytoplasm can be used to avoid degradation of the complex by intracellular lysosomes (see for example Curiel et al. (1991) Proc. Natl. Acad. Sci. USA 88:8850; Cristiano et al. (1993) Proc. Natl. Acad. Sci. USA 90:2122-2126).

Retroviruses: Defective retroviruses are well characterized for use in gene transfer for gene therapy purposes (for a review see Miller, A. D. (1990) Blood 76:271). A recombinant retrovirus can be constructed having a nucleotide sequences of interest incorporated into the retroviral genome. Additionally, portions of the retroviral genome can be removed to render the retrovirus replication defective. The replication defective retrovirus is then packaged into virions which can be used to infect a target cell through the use of a helper virus by standard techniques. Protocols for producing recombinant retroviruses and for infecting cells in vitro or in vivo with such viruses can be found in Current Protocols in Molecular Biology, Ausubel, F. M. et al. (eds.) Greene Publishing Associates, (1989), Sections 9.10-9.14 and other standard laboratory manuals. Examples of suitable retroviruses include pLJ, pZIP, pWE and pEM which are well known to those skilled in the art. Examples of suitable packaging virus lines include ψ Crip, ψCre, ψ2 and ψAm. Retroviruses have been used to introduce a variety of genes into many different cell types, including epithelial cells, endothelial cells, lymphocytes, myoblasts, hepatocytes, bone marrow cells, in vitro and/or in vivo (see for example Eglitis, et al. (1985) Science 230:1395-1398; Danos and Mulligan (1988) Proc. Natl. Acad. Sci. USA 85:6460-6464; Wilson et al. (1988) Proc. Natl. Acad. Sci. USA 85:3014-3018; Armentano et al. (1990) Proc. Natl. Acad. Sci. USA 87:6141-6145; Huber et al. (1991) Proc. Natl. Acad. Sci. USA 88:8039-8043; Ferry et al. (1991) Proc. Natl. Acad. Sci. USA 88:8377-8381; Chowdhury et al. (1991) Science 254:1802-1805; van Beusechem et al. (1992) Proc. Natl. Acad. Sci. USA 89:7640-7644; Kay et al. (1992) Human Gene Therapy 3:641-647; Dai et al. (1992) Proc. Natl. Acad. Sci. USA 89:10892-10895; Hwu et al. (1993) J. Immunol. 150:4104-4115; U.S. Pat. No. 4,868,116; U.S. Pat. No. 4,980,286; PCT Application WO 89/07136; PCT Application WO 89/02468; PCT Application WO 89/05345; and PCT Application WO 92/07573). Retroviral vectors require target cell division in order for the retroviral genome (and foreign nucleic acid inserted into it) to be integrated into the host genome to stably introduce nucleic acid into the cell. Thus, it may be necessary to stimulate replication of the target cell.

Adenoviruses: The genome of an adenovirus can be manipulated such that it encodes and expresses a gene product of interest but is inactivated in terms of its ability to replicate in a normal lytic viral life cycle. See for example Berkner et al. (1988) BioTechniques 6:616; Rosenfeld et al. (1991) Science 252:431-434; and Rosenfeld et al. (1992) Cell 68:143-155. Suitable adenoviral vectors derived from the adenovirus strain Ad type 5 d1324 or other strains of adenovirus (e.g., Ad2, Ad3, Ad7 etc.) are well known to those skilled in the art. Recombinant adenoviruses are advantageous in that they do not require dividing cells to be effective gene delivery vehicles and can be used to infect a wide variety of cell types, including airway epithelium (Rosenfeld et al. (1992) cited supra), endothelial cells (Lemarchand et al. (1992) Proc. Natl. Acad. Sci. USA 89:6482-6486), hepatocytes (Herz and Gerard (1993) Proc. Natl. Acad. Sci. USA 90:2812-2816) and muscle cells (Quantin et al. (1992) Proc. Natl. Acad. Sci. USA 89:2581-2584). Additionally, introduced adenoviral DNA (and foreign DNA contained therein) is not integrated into the genome of a host cell but remains episomal, thereby avoiding potential problems that can occur as a result of insertional mutagenesis in situations where introduced DNA becomes integrated into the host genome (e.g., retroviral DNA). Moreover, the carrying capacity of the adenoviral genome for foreign DNA is large (up to 8 kilobases) relative to other gene delivery vectors (Berkner et al. cited supra; Haj-Ahmand and Graham (1986) J. Virol. 57:267). Most replication-defective adenoviral vectors currently in use are deleted for all or parts of the viral E1 and E3 genes but retain as much as 80% of the adenoviral genetic material.

Adeno-Associated Viruses: Adeno-associated virus (AAV) is a naturally occurring defective virus that requires another virus, such as an adenovirus or a herpes virus, as a helper virus for efficient replication and a productive life cycle. (For a review see Muzyczka et al. Curr. Topics in Micro. and Immunol. (1992) 158:97-129). It is also one of the few viruses that may integrate its DNA into non-dividing cells, and exhibits a high frequency of stable integration (see for example Flotte et al. (1992) Am. J. Respir. Cell. Mol. Biol. 7:349-356; Samulski et al. (1989) J. Virol. 63:3822-3828; and McLaughlin et al. (1989) J. Virol. 62:1963-1973). Vectors containing as little as 300 base pairs of AAV can be packaged and can integrate. Space for exogenous DNA is limited to about 4.5 kb. An AAV vector such as that described in Tratschin et al. (1985) Mol. Cell. Biol. 5:3251-3260 can be used to introduce DNA into cells. A variety of nucleic acids have been introduced into different cell types using AAV vectors (see for example Hermonat et al. (1984) Proc. Natl. Acad. Sci. USA 81:6466-6470; Tratschin et al. (1985) Mol. Cell. Biol. 4:2072-2081; Wondisford et al. (1988) Mol. Endocrinol. 2:32-39; Tratschin et al. (1984) J. Virol. 51:611-619; and Flotte et al. (1993) J. Biol. Chem. 268:3781-3790).

The efficacy of a particular expression vector system and method of introducing nucleic acid into a cell can be assessed by standard approaches routinely used in the art. For example, DNA introduced into a cell can be detected by a filter hybridization technique (e.g., Southern blotting) and RNA produced by transcription of introduced DNA can be detected, for example, by Northern blotting, RNase protection or reverse transcriptase-polymerase chain reaction (RT-PCR). The gene product can be detected by an appropriate assay, for example by immunological detection of a produced protein, such as with a specific antibody, or by a functional assay to detect a functional activity of the gene product.

In a preferred embodiment, a retroviral expression vector encoding human MEKK is used to express human MEKK protein in cells in vivo, to thereby stimulate MEKK protein activity in vivo. Such retroviral vectors can be prepared according to standard methods known in the art (discussed further above).

A modulatory agent, such as a chemical compound, can be administered to a subject as a pharmaceutical composition. Such compositions typically comprise the modulatory agent and a pharmaceutically acceptable carrier. As used herein the term “pharmaceutically acceptable carrier” is intended to include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the compositions is contemplated. Supplementary active compounds can also be incorporated into the compositions. Pharmaceutical compositions can be prepared as described above in subsection IV.

This invention is further illustrated by the following example, which should not be construed as limiting. The contents of all references, patents and published patent applications cited throughout this application are hereby incorporated by reference. Additionally, all nucleotide and amino acid sequences deposited in public databases referred to herein are also hereby incorporated by reference.

EXAMPLE 1 Isolation and Characterization of a Human MEKK1 Nucleic Acid

The following strategy was used to identify the nucleic acid sequence encoding human MEKK1.

cDNA Preparation—Total mRNA was extracted and isolated from T47D cells using 1×10⁷ cells per purification in the QuickPrep Micro mRNA Purification Kit (Pharmacia). First strand cDNA was produced using 33 microliters of the purified mRNA per reaction in the Ready-to-Go T-Primed First-Strand Kit (Pharmacia).

PCR Amplification—The sense strand primer 5′-GAACACCATCCAGAAGTTTG-3′ (SEQ ID NO: 14), which was designed from the mouse MEKK1 (mMEKK1) cDNA sequence, was used in conjunction with the antisense primer 5′-CACTTTGTAGACAGGGTCAGC-3′ (SEQ ID NO: 15) in a polymerase chain reaction (PCR) using the first strand cDNA described above as a template (RT-PCR) to amplify the region from bases 1211-1950. Taq DNA Polymerase (Boehringer Mannheim) was used in a RT-PCR of 30 cycles (1 min. 94° C.; 1 min. 50° C.; 3 min., 72° C.), followed by a 10 min. incubation at 72° C. A band of approximately 800 bp was isolated by purification from a 1% agarose gel and ligated overnight at 14° C. into pGEM-T coli by heat shock at 42° C., and plated on Luria Broth (LB) plates containing ampicillin and X-gal. Colonies were screened by blue/white color selection, grown up in 5 ml of LB containing ampicillin, and the plasmid DNA was isolated using the Wizard Mini-pre Kit (Promega). Isolates were then screened for insert size by digesting with PstI and AatII (Promega), and running on a 1% agarose gel. Appropriately sized inserts were sequenced from both ends using T7 and SP6 vector primers. The resulting sequence was aligned to the known mMEKK1 sequence, and determined to be hMEKK1 by homology. In order to amplify the region from bases 2263-3743, the sense primer 5′-TGGGTCGCCTCTGTCTTATAGACAG-3′ (SEQ ID NO: 16) was used in conjunction with the antisense primer 5′-CACATCCTGTGCTTGGTAAC-3′ (SEQ ID NO: 17) in a RT-PCR of 30 cycles (1 min. 94° C.; 1 min., 50° C.; 2 min., 72° C.), followed by a 10 min. incubation at 72° C. A band of approximately 1.5 kb was isolated by purification from a 1% agarose gel, ligated, cloned, and sequenced as stated above. In order to amplify the 3′ region of hMEKK1 from bases 3304-4493, the sense primer 5′-AGGACAAGTGCAGGTTAGATG-3′ (SEQ ID NO: 18) was used in a RT-PCR of 30 cycles (1 min., 94° C.; 1 min., 50° C.; 2 min., 72° C.), followed by a 10 min. incubation at 72° C. A band of approximately 1.3 kb was isolated by purification from a 1% agarose gel, ligated, cloned, and sequenced as stated above. Sequence was also confirmed for this clone using the internal sequencing primer 5′-GCTGTCCATATCTACAGTGCT-3′ (SEQ ID NO: 19). In order to amplify the region from bases 580-1310, the sense primer 5′-CGGCCTGGAAGCACGAGTGGT-3′ (SEQ ID NO: 20) was used in conjunction with the antisense primer 5′-TTCATCCTTGATGCTGTTTTC-3′ (SEQ ID NO: 21) in a RT-PCR of 30 cycles (1 min., 94° C.; 1 min., 50° C.; 2 min., 72° C.), followed by a 10 min. incubation at 72° C. A band of approximately 700 bp was isolated by purification from a 1% agarose gel, ligated, cloned, and sequenced as stated above. The overlapping sequence data was compiled into a single contig using Sequencer 2.0 (Gene Codes), and aligned to the mMEKK1 sequence (FIG. 3). The nucleotide and predicted amino acid sequences of human MEKK3 are shown in FIGS. 1 and 2, respectively. FIG. 4 depicts an alignment of the amino acid sequences of hMEKK1 and mMEKK1. Amino acid differences between the two proteins are indicated by bold underlining.

A BLASTN search using the nucleotide sequence of human MEKK1 as described in this example reveals the following nucleic acid sequences having homology to that set forth in SEQ ID NO:1: GenBank Accession Nos. L13103, U23470, AF042838, and U48596, having 96%, 96%, 95%, and 89% identity to SEQ ID NO: 1, respectively.

A BLASTP search using the amino acid sequence of human MEKK1 as described in this example reveals the following amino acid sequences having homology to that set forth in SEQ ID NO:2: Swiss-Prot Accession No. Q62925, having 82% identity to SEQ ID NO:2; GenBank Accession No. AF042838, having 81% identity to SEQ ID NO:2; and GenBank Accession No. P53349, GenBank Accession No. U23470, PIR Accession No. A46212, and GenBank Accession No. L13103, each having 91% identity to SEQ ID NO:2; , having 91% identity to SEQ ID NO:2.

EXAMPLE 2 Isolation and Characterization of a Human MEKK2 Nucleic Acid

The following strategy was used to identify the nucleic acid sequence encoding human MEKK2.

cDNA Preparation—Total mRNA was extracted and isolated from T47D cells using 1×10⁷ cells per purification in the QuickPrep Micro mRNA Purification Kit (Pharmacia). First strand cDNA was produced using 33 microlitres of the purified mRNA per reaction in the Ready-To-Go T-Primed First-Strand Kit (Pharmacia).

PCR Amplification—The sense strand primer 5′-GGCCAGCTCGGTGGCCT-3′ (SEQ ID NO: 22), which annealed to the 5′ untranslated region of human MEKK2 (hMEKK2), was designed from the mouse MEKK2 (mMEKK2) cDNA sequence, and used in conjunction with the antisense primer 5′-TCTGGAATGTATCCTGG-3′ (SEQ ID NO: 23) in a polymerase chain reaction (PCR) using the first strand cDNA described above as a template (RT-PCR). Taq DNA Polymerase (Boehringer Mannheim) was used in a RT-PCR of 30 cycles (1 min, 94° C.; 1 min, 50° C.; 3 min, 68° C.), followed by 10-min incubation at 72° C. One microlitre of the resulting reaction mixture was used as a template for a second PCR under the same conditions, and one microlitre of the secondary reaction mixture was used as a template again in a third PCR under the same conditions. A band of approximately 600 bp was isolated by purification from a 1% agarose gel and ligated overnight at 14° C. into pCR2.1 using the Original T/A Cloning Kit (Invitrogen). The ligation mixture was transformed by heat shock of the E. coli strain TOP10F′ at 42° C., and plated on Luria Broth (LB) plates containing ampicillin and X-gal. Colonies were screened by blue/white color selection, grown up in 5 ml of LB containing ampicillin, and the plasmid DNA was isolated using Mini-Prep Spin Columns (Qiagen). Isolates were then screened for insert size by digesting with EcoRI (Gibco/BRL), and running on a 1% agarose gel. Appropriately sized inserts were sequenced from both ends using M13 Forward and Reverse vector primers. The resulting sequence was aligned to the known mMEKK2 sequence, and determined to be hMEKK2 by homology. After sequencing the 5′ portion of hMEKK2, the sense primer 5′-AGAGAGGAAAAAGCGGC-3′ (SEQ ID NO: 24), which annealed to a region that overlapped the previously sequenced portion of hMEKK2, was used in conjunction with the two antisense primers 5′-CAGCCAGCTCTCTTCCG-3′ (SEQ ID NO: 25) and 5′-GGAAAAGTCTTCCGACC-3′ (SEQ ID NO: 26) in two separate RT-PCR of 30 cycles (1 min, 94° C.; 1 min, 50° C.; 2 min, 68° C.), followed by a 10-min incubation at 72° C. One microlitre of the resulting reaction mixtures was used as a template for two separate second PCR under the same conditions. Two bands of approximately 700 bp and 400 bp respectively were isolated by purification from a 1% agarose gel, ligated, cloned, and sequenced as stated above. In order to sequence the 3′ portion of hMEKK2, the sense primer 5′-GGCCAAGGAGCTTTTGGTAGG-3′ (SEQ ID NO: 27), which annealed to a region that overlapped the previously sequenced region of hMEKK2, was used in conjunction with the antisense primer 5′-GGAGCTGGTGGAGGACCGAAG-3′ (SEQ ID NO: 28), which annealed to the 3′ untranslated region of hMEKK2, in a RT-PCR of 30 cycles (1 min, 94° C.; 1 min, 50° C.; 2 min, 68° C.), followed by a 10-min incubation at 72° C. One microlitre of the resulting reaction mixture was used as a template for a second PCR under the same conditions. A band of approximately 750 bp was isolated by purification from a 1% agarose gel, ligated, cloned, and sequenced as stated above. The overlapping sequence data was compiled into a single contig using Sequencher 2.0 (Gene Codes), and aligned to the mMEKK2 sequence (FIG. 7). The nucleotide and predicted amino acid sequences of human MEKK3 are shown in FIGS. 5 and 6, respectively. FIG. 8 depicts an alignment of the amino acid sequences of hMEKK2 and mMEKK2. Amino acid differences between the two proteins are indicated by bold underlining.

A BLASTN search using the nucleotide sequence of human MEKK2 as described in this example reveals that a nucleic acid molecule having GenBank Accession No. U43186 has 98% identity to the human MEKK2 nucleic acid sequence set forth as SEQ ID NO:3. A BLASTP search using the human MEKK2 amino acid sequence set forth in SEQ ID NO:4 reveals the following proteins having homology to human MEKK2: Swiss Prot Accession Nos. Q61083, Q61084, and Q99759, having 90%, 63% and 63% identity, respectively.

EXAMPLE 3 Isolation and Characterization of a Human MEKK3 Nucleic Acid

To isolate a nucleic acid molecule encoding human MEKK3, the sense primer 5′-CCCAGAACCCTGGCCGAAGCT-3′ (SEQ ID NO: 29), which annealed to a region in the middle of human MEKK3 (hMEKK3), was designed from the mouse MEKK3 (mMEKK3) cDNA sequence and used in conjunction with the antisense primer 5′-AGCACGGTCCCGCAGGCAGCC-3′ (SEQ ID NO: 30). Taq DNA Polymerase (Boehringer Mannheim) was used in a RT-PCR of 30 cycles (1 min, 94° C.; 1 min, 50° C.; 3 min, 72° C.), followed by a 10-min incubation at 72° C. using Marathon Ready™ human bone marrow, placental, and testis cDNA (Clontech) as templates. A band of approximately 800 bp was isolated from testis and placental template reactions by purification from a 1% agarose gel and ligated overnight at 14° C. into pCR2.1 using the Original T/A Cloning Kit (Invitrogen). The ligation mixture was transformed by heat shock of the E. coli strain TOP10F′ at 42° C., and plated on Luria Broth (LB) plates containing ampicillin, IPTG and X-gal. Colonies were screened by blue/white color selection, grown up in 5 ml of LB containing ampicillin, and the plasmid DNA was isolated using Mini-Prep™ Spin Columns (Qiagen). Isolates were then screened for insert size by digesting with EcoRI (Gibco/BRL), and running on a 1% agarose gel. Appropriately sized inserts were sequenced from both ends using M13 Forward and Reverse vector primers. The resulting sequence was aligned to the known mMEKK3 sequence, and determined to be hMEKK3 by homology. In order to sequence the 5′ end of hMEKK, the sense strand primer 5′-GTAGTCGCCACCGCCGCCTCC-3′ (SEQ ID NO: 31), which annealed to the 5′ untranslated region of hMEKK3, was designed from the mMEKK3 cDNA sequence, and used in conjunction with the antisense primer 5′-CTGACAAGGAATTTTCGGCAC-3′ (SEQ ID NO: 32) which overlapped the previously sequenced portion of hMEKK3, in a RT-PCR of 30 cycles (1 min, 94° C.; 1 min, 50° C.; 3 min, 72° C.) in seven different buffers of varying pH and magnesium concentrations, followed by a 10-min incubation at 72° C. One microlitre of the resulting reaction mixture were used as a template for a second PCR under the same conditions with the nested sense strand oligo 5′-ACCGCCGCCTCCGCCATCGCC-3′ (SEQ ID NO: 33) and the nested antisense strand oligo 5′-CACTGTTCGCTGGTCTCTGGG-3′ (SEQ ID NO: 34). A band of approximately 700 bp was isolated from the reaction mixture buffered with 17.5 mM MgCl₂ at pH 8.5 by purification from a 1% agarose gel, ligated, cloned, and sequenced as stated above. In order to sequence the 3′ portion of hMEKK3, the sense primer 5′-AGACAAGCAAGGAGGTGAGTG-3′ (SEQ ID NO: 35), which annealed to a region that overlapped the previously sequenced region of hMEKK3, was used in conjunction with the antisense primer 5′-GCCTGACAGCAGCCCCTTGCC-3′ (SEQ ID NO: 36), which annealed to the 3′ untranslated region of hMEKK3, in a RT-PCR of 30 cycles (1 min, 94° C.; 1 min, 50° C.; 2 min, 72° C.), followed by a 10-min incubation at 72° C. Subsequently, the nested sense primer 5′-TCCAGTTGCTAAAGAACTTGC-3′ (SEQ ID NO: 37) was used in conjunction with the nested antisense primer 5′-TGGCAGCTGGCAGCCTGATAG-3′ (SEQ ID NO: 38) in a secondary RT-PCR of 30 cycles (1 min, 94° C.; 1 min, 50° C.; 2 min, 72° C.), followed by a 10-min incubation at 72° C. A band of approximately 670 bp was isolated by purification from a 1% agarose gel, ligated, cloned, and sequenced as stated above. The overlapping sequence data was compiled into a single contig using Sequencher 2.0 (Gene Codes), and aligned to the mMEKK3 sequence (FIG. 11). The nucleotide and predicted amino acid sequences of human MEKK3 are shown in FIGS. 9 and 10, respectively. FIG. 12 depicts an alignment of the amino acid sequences of hMEKK3 and mMEKK3. Amino acid differences between the two proteins are evident, which differences are underlined and bolded.

A BLASTN search using the nucleic acid sequence of human MEKK3 reveals the following nucleic acid molecules having homology to SEQ ID NO:5: GenBank Accession Nos. U43187 and U78876, having 95% and 93% identity, respectively. A BLASTP search using the human MEKK3 amino acid sequence set forth in SEQ ID NO:6 reveals the following proteins having homology to human MEKK3: Swiss Prot Accession Nos. Q61084, Q99759, and Q61083, having 97%, 95%, and 62% identity to SEQ ID NO:6.

EXAMPLE 4 Antibodies to human MEKK proteins

Peptides corresponding to COOH-terminal sequence of a human MEKK protein (e.g., amino acids 1280-1300 of SEQ ID NO:2, amino acids 599-617 of SEQ ID NO:4, or amino acids 605-623 of SEQ ID NO:6) are conjugated to keyhole limpet hemocyanin and used to immunize rabbits. Antisera are characterized for specificity by immunoblotting of lysates prepared from appropriately transfected HEK293 cells.

EXAMPLE 4 Assays of Activity of MEKK and Downstream Signaling Molecules

Assay of JNK Activity—JNK activity is measured using GST (glutathione S-transferase)-c-Jun₍₁₋₇₉₎ coupled to glutathione-Sepharose 4B (M. Hibi et al., Genes & Dev.; 7:2135-2148 (1993)). Cells transfected with MEEK3 and control transfected cells are lysed in 0.5% Nonidet P-40, 20 mM Tris-HCL, pH 7.6, 0.25 M NaCl, 3 mM EDTA, 3 mM EGTA, 1 mM dithiothreitol, 1 mM phenymethylsulfonyl fluoride, 2 mM sodium vanadate, 20 μg/ml aprotinin, and 5 μg/ml leupeptin. Nuclei are removed by centrifugation at 15,000×g for 10 min., and the supernatants (25 μg of protein) are mixed with 10 μl of slurry of GST-c-Jun₍₁₋₇₉₎-Sepharose (3-5 μg of GST-c-Jun₍₁₋₇₉₎. The mixture is rotated at 4° C. for 1 h, washed trice in lysis buffer and once in kinase buffer (20 mM Hepes, pH 7.5, 10 mM MgCl₂, 20 mM β-glycerophosphate, 10 mM p-nitrophenyl phosphate, 1 mM dithiothreitol, 50 μM sodium vanadate). Beads are suspended in 40 μl of kinase assay buffer containing 10 μCi of [γ-³²P]ATP and incubated at 30° C. for 20 minutes. Reactions mixtures are added to Laemmli sample buffer, boiled, and phosphorylated proteins are resolved on SDS-01% polyacrylamide gels. When JNK activity is assayed following fractionation by Mono Q ion exchange chromatography, 50 μl of each fraction is incubated with the GST-c-Jun₍₁₋₇₉₎ beads.

p42/44^(MAPK) Assay—MAPK activity following Mono Q FPLC fractionation is measured as described in L. E. Heasley et al., Mol. Biol. Cell; 3:545-533 (1992) using the epidermal growth factor receptor 662-681 peptide as a selective p42/44^(MAPK) substrate (M. Russell et al., Biochemistry; 34:6611-6615 (1995)). Alternatively, for cells transfected with varying amounts of MEKK plasmids MAPK activity is assayed after elution from DEAE-Sephacel columns (L. E. Heasley et al., Am. J. Physiol.; 267:F366-F373 (1994)).

Assay of MEKK Kinase Activity in Vitro—To assay MEKK activity in vitro, immune complexes are incubated with recombinant wild type or kinase-inactive MEK 1 (Lys⁹⁷→Met) or JNKK (Lys¹¹⁶→Arg) as a substrate (A. Lin et al, Science; 268:286-290 (1995), C. A. Lange-Carter et al, Science; 265:1458-1461 (1994), M. Russell et al., Biochemistry; 34:6611-6615 (1995)). Transfected HEK293 cells are lysed in 1% Triton X-100, 0.5% Nonidet P-40, 20 mM Tris-HCl, pH 7.5, 150 mM NaCL, 20 mM NaF, 0.2 mM sodium vanadate, 1 mM EDTA, 1 mM EGTA, 5 mM phenylmethylsulfonyl fluoride. Nuclei are removed by centrifugation at 15,000×g for 5 min. HA epitope-tagged MEKK are immunoprecipitated with the 12CA5 antibody and protein A-Sepharose (B. E. Wadzinski et al., J. Biol. Chem.; 267:16883-16888 (1992), N.-X. Qian et al., Proc. Natl. Acad. Sci. U.S.A.; 90:4077-4081 (1993)). Immunoprecipitates are washed twice in lysis buffer, twice in 20 mM Pipes, 10 mM MnCl₂, 20 μg/ml aprotinin, and used in an in vitro kinase assay with 20-50 ng of recombinant MEK 1 or JNKK as substrates and 20 μCi of [γ-³²P]ATP (M. Russell et al., Biochemistry; 34:6611-6615 (1995)). Reactions are terminated by the addition of Laemmli sample buffer, boiled, and proteins are resolved by SDS-10% polyacrylamide gel electrophoresis.

To demonstrate MEKK activation of JNKK activity, the in vitro kinase reactions are performed with different combinations of recombinant wild type or kinase-inactive JNK. Kinase-inactive NJK is made by mutating the active site lysine 55 to methionine. Incubations are for 30 min. at 30° C. in the presence of 50 μM ATP. GST-c-Jun₍₁₋₇₉₎-Sepharose beads are then added, and the mixture is rotated at 4° C. for 30 minutes. The beads are washed, suspended in 40 μl of c-Jun kinase assay buffer containing 20 μCi of [γ-³²P]ATP, and incubated for 15 min. at 30° C. Reaction mixtures are added to Laemmli sample buffer, boiled, and phosphorylated proteins are resolved in SDS-10% polyacrylamide gels.

Assay of p38 Kinase Activity—Sorbitol-treated (0.4 M, 20 min.) or control HEK293 cells are lysed in the same buffer as that used for assay of MEKK. Supernatants (200 μg of protein) are used for COOH-terminal peptide sequence of p38 (J. Han et al, Science; 265:8-8-811 (1994)). Immunoprecipitates are washed once in lysis buffer, once in assay buffer (25 mM Hepes, pH 7.4, sodium vanadate), resuspended, and used in an in vitro kinase assay susbstrate and 20 μCi of [γ-³²P]ATP (H. Abdel-Hafez et al., Mol. Endocrinology; 6:2079-2089 (1992)). For analysis of p38 kinase activity from Mono Q FPLC fractions, 20 μl aliquots are mixed with kinase buffer containing 20-50 ng of recombinant ATF 2 and 10 μCi of [γ-³²P]ATP (M. Russell et al., Biochemistry; 34:6611-6615 (1995), H. Abdel-Hafez et al., Mol. Endocrinology; 6:2079-2089 (1992)). Reactions are quenched in Laemmli sample buffer, boiled, and proteins are resolved using SDS-10% polyacrylamide gels.

Equivalents

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims. 

1. Antibodies that specifically bind human MEKK protein.
 2. The antibodies of claim 1, which are polyclonal antibodies.
 3. The antibodies of claim 1, which are monoclonal antibodies.
 4. The antibodies of claim 1, which are coupled to a detectable substance.
 5. A nonhuman transgenic animal that contains cells carrying a transgene encoding a human MEKK protein.
 6. A method for detecting the presence of human MEKK in a biological sample comprising contacting the biological sample with an agent capable of detecting an indicator of human MEKK activity such that the presence of human MEKK is detected in the biological sample.
 7. A method for modulating human MEKK activity in a cell comprising contacting the cell with an agent that modulates human MEKK activity such that human MEKK activity in the cell is modulated.
 8. A cell in which expression of a signal transduction polypeptide is lacking due to targeted disruption of a gene encoding the signal transduction polypeptide.
 9. A cell in which mitogen-activated protein kinase/extracellular response kinase (MAPK/ERK) kinase kinase1 (MEKK1) is lacking due to at least one mutation having been introduced into each allele of the gene encoding MEKK1.
 10. A method for regulating a human MEKK-dependent process in a human cell comprising contacting the cell with an agent that modulates human MEKK activity such that human MEKK activity in the cell is modulated. 